LIBRARY 


UNIVERSITY  OF  CALIFORNIA. 


Class 


OTES  ON  ASSAYING 


AND 


METALLURGICAL    LABORATORY 
EXPERIMENTS. 


BY 


RICHARD  W.  LODGE, 

u 

\stant  Professor  of  Mining  and  Metallu 
Massachusetts  Institute  of  Technology. 


SECOND   EDITION,  REVISED. 
FIRST   THOUSAND. 


NEW  YORK : 

JOHN  WILEY  &  SONS. 

LONDON:  CHAPMAN  &  HALL,  LIMITED. 

1906 


Copyright,  1904,  1906* 

BY 
R.  W.   LODGE. 


•OBERT  DRUMMOND,   PRINTER,  NBW  YORK. 


PREFACE. 


IN  this  book  I  have  combined  the  notes  which  have  been  in 
use  for  many  years  by  the  third-year  students  in  Assaying  and 
fart  of  the  notes  used  by  the  fourth-year  students  in  the  Metal- 
lurgical Laboratory  of  the  Massachusetts  Institute  of  Technology. 

Many  new  data  and  experiments  carried  out  by  my  assistants^ 
by  former  students,  and  by  myself,  which  have  been  accumulating, 
have  now  been  added.  The  notes  are  written  especially  for  the 
use  of  the  students  of  the  Institute  and  for  those  who  are  com- 
mencing assaying,  but  it  is  hoped  that  persons  well  versed  in 
laboratory  work  and  actual  practice  may  also  derive  some  infor- 
mation from  them.  At  the  laboratory,  in  the  Institute,  students 
are  expected  to  use  these  notes  on  the  work  assigned,  preceding 
and  accompanying  which  lectures  are  given. 

In  treating  of  the  assay  for  the  metals,  I  have  endeavored  to 
give  first  what  I  consider  the  best  method  or  methods,  with  re- 
agents, the  amount  used,  and  the  reasons  for  using  them.  The 
student  thus  becomes  familiar  with  my  way  of  working.  After 
this  are  given  the  methods  used  or  recommended  by  others. 

The  reagents  and  fluxes  are  given  as  Mitchell  groups  them, 
for  his  method  seems  the  simplest  and  most  systematic. 

I  have  consulted  the  best  works  upon  the  subject,  such  as  those 
by  Berthier,  Mitchell,  Furman,  Brown,  Beringer,  and  Ricketts; 
any  indebtedness  to  whom  I  wish  to  acknowledge. 

The  manner  of  conducting  the  larger  laboratory  tests,  here 
discussed,  is  based  on  many  experiments  and  at  present  seems 
to  be  the  best  way  to  introduce  students  to  metallurgical  work 
on  a  large  scale. 

I  wish  especially  to  thank  for  their  loyalty  and  aid  those 
who  have  been  my  assistants  and  many  former  students. 

R.  W.  LODGE. 

MASSACHUSETTS  INSTITUTE  OF  TECHNOLOGY, 
September,  1904. 

iii 


HOB 


CONTENTS. 


CHAPTER  I. 

PAG& 

APPARATUS,  REAGENTS,  MATERIALS r 

Balances. 

Weights.    Assay  Ton  System. 

Memoranda  as  to  Weights  and  Values. 

Assay  Reagents.  Reducing  Agents.  Oxidizing  Agents.  De- 
sulphurizing Agents.  Sulphurizing  Agents.  Fluxes. 

Fusion  Products.     Slag.    Matte  or  Regulus.    Speiss. 

Furnaces  and  Fuels. 

Refractories.  Fire-clays.  Fire-brick.  Crucibles.  Graphite 
Crucibles.  Scarifiers.  Cupels.  Muffles. 

Mortars  and  Lutes. 


CHAPTER  H. 

SAMPLING 25- 

Labelling  Samples.  Methods  of  Sampling.  Ores  Carrying 
Metallic  Particles. 

Concentration  by  Panning  or  Vanning. 

CHAPTER  III. 

ASSAY  OF  ORES  FOR  SILVER 39, 

Scorification  Method.     Essentials  in  Process.    Reactions. 

Amount  of  Lead  Required  for  Different  Ores.  Rescorifying 
Buttons.  Spitting  of  Ores  during  Scorification.  Assay  of  Zinc 
Residues. 

Assay  of  Copper  Matte.  Assay  of  Copper  and  Copper  Bars. 
Combination  Wet  and  Dry  Method. 

Cupellation.  Reactions.  Experiment  with  C.P.  Silver.  Sil- 
ver Losses.  Effect  of  Different  Temperatures.  Effect  of  Varying 
the  I>ad.  Effect  of  Copper.  Effect  of  Tellurium. 


vi  CONTENTS. 

Crucible  Method. 

Fluxes  and  Reagents. 

Effect  of  Fluxes  at  High  Temperature  on  Different  Substances. 

Sulphates.     Action  in  Presence  of  Litharge  and  of  Lead  Sulphate. 

Testing  Reagents.  Assay  of  Granulated  Lead.  Assay  of  Lith- 
arge. Oxidizing  Power  of  Nitre. 

Reducing  Agents.  Fusion  for  Reducing  Power.  Influence  of 
Other  Reagents  on  this  Fusion. 

Regular  Assay.  Silicious  and  Oxide  Ores  (Class  I).  Fusion 
in  Pot-furnace.  Fusion  in  Muffle-furnace. 

Sulphide  Ores  or  Those  with  a  Reducing  Power  (Class  II). 
Preliminary  Fusion  for  the  Reducing  Power.  Influence  of  Reagents 
(Silica,  .Eorax,  Borax-glass,  and  Soda)  on  the  Reducing  Power. 
Effect  of  Temperature. 

Regular  Fusion.     Effect  of  Silica  on  the  Fusion.      Iron  Method. 
Effect  of  Temperature.    Ores  containing  Organic  Matter.    Size 
of  Lead  Buttons.     Dusting  of  Ores. 

Special  Methods.  Copper  Ores.  Antimonial  Ores.  Pyrrhotite. 
Ores  Carrying  Barite. 

CHAPTER   IV. 

ASSAY  OF  ORES  FOR  GOLD 127 

Occurrence  of  Ores.     Steps  in  Assay. 

Class  I.  Ores  with  no  Reducing  Power.  Scorification  Method. 
Crucible  Method.  Fusion  in  the  Pot-furnace.  Fusion  in  the 
Muffle. 

Class  II.  Ores  with  a  Reducing  Power.  Scorification  Method. 
Method  of  Roasting  the  Ore.  Iron  Method.  Assay  of  Arsenical 
Ores.  Litharge  and  Nitre  Method. 

Class  III.  Telluride  Ores.  Effect  of  Tellurium  upon  Cupella- 
tion  of  Gold. 

Cupelling  and  Weighing  the  Beads  of  Precious  Metals. 

Parting.     Separation  of  Gold  from  Platinum  and  Iridium. 

Experiment  in  Roasting  an  Ore  or  Concentrates. 

Cupellation  of  Gold  at  Different  Temperatures.  Effect  of 
Copper. 

Special  Methods.  Assay  of  Zinc-box  Residues  by  Scorification. 
Crucible  Assays.  Copper  Matte,  Copper  Ears,  and  Copper.  Com- 
bination Wet  and  Dry  Method. 

Gold  and  Silver  in  Antimony.  Gold  and  Silver  in  Metallic 
Bismuth. 

Assaying  Solutions. 


CONTENTS.  vii 

CHAPTER  V. 

PAGB 

ASSAY  OF  ORES  FOR  LEAD  ............................  .  ............  190 

Lead  Ores. 

Sulphide  Ores.  Fusion  in  the  Muffle.  Cyanide  of  Potash 
Method.  Fusion  in  the  Pot-furnace.  Slags  and  Furnace  Products. 
Ores  Very  Poor  in  Lead.  Fusion  in  Iron  Crucible. 

Ores  Containing  no  Sulphides. 

General  Remarks  upon  the  Lead  Assay. 

CHAPTER  VI. 

BULLION  ........................................................  19$ 

Lead  Bullion  or  Base  Bullion. 

Silver  Bullion  Containing  no  Gold.  Silver  Bullion  Containing 
Gold.  Wet  Methods. 

Recovery  of  Silver  from  Solutions. 
Gold  Bullion. 


CHAPTER 

ASSAY  OF  ORES  FOR  COPPER  AND  TIN  ..............................  213 

Copper  Assay. 

Ores  of  Copper.  Sulphide  Ores.  Oxide  and  Carbonate  Ores. 
Native  Copper  Ores. 

Assay  of  Sulphide  Ores  (Class  I).  Roasting.  Fusion.  Re- 
fining Flux. 

Assay  of  Oxide  and  Carbonate  Ores  (Class  II). 

Assay  of  Ores  Carrying  Native  Copper  (Class  III). 

Assay  of  Ores  for  Tin. 

Tin  Deposits.     Ores. 

Steps  in  the  Assay.  Concentration.  Roasting.  Treatment  with 
Acid.  Panning.  Assaying. 

Methods  of  Assaying.  Cyanide  of  Potash  Method.  German 
Assay.  Assay  with  Sodium  Carbonate  and  Lime.  Assay  in  Graphite 
Crucible. 

CHAPTER  VIII. 

PLATINUM  AND  THE  PLATINUM  GROUP  ..............................  224 

The  Platinum  Group. 

Occurrence  of  Platinum.  Sources.  Qualitative  Tests.  Quan- 
titative Analysis. 


CONTENTS. 

PAGI 

Table  of  Solubility  of  the  Group. 

Assay  of  Sands  and  Ores.  Tree  of  the  Treatment.  Determina- 
tion of  Silver,  Gold,  Platinum,  Indium,  and  Iridosmium 

Platinum  and  Silver  Alloys.  Different  Ratios  of  Platinum  and 
Silver  and  their  Solubility  in  Nitric  Acid  of  Different  Strengths. 

Platinum,  Silver,  and  Gold  Alloys  and  their  Solubility  in  Nitric 
Acid. 

Platinum.  Iridium.  Palladium.  Osmium.  Ruthenium. 
Iridosmium. 


METALLURGICAL      LABORATORY      EXPERIMENTS     AND 

NOTES. ! 243 

General  Directions. 

Solutions.     Calcining.     Roasting. 

Chlorination  of  Gold  Ores.  Plattner  Process.  Effect  of  Impurities 
upon  the  Precipitation  of  Gold  from  AuCl3.  Barrel  Process. 

Cyanide  Process  for  Treatment  of  Gold  Ores.  Cyanide  Process  as 
Applied  to  Concentrates  from  Nova  Scotia.  Reactions  in  the  Process. 
Testing  a  Roasted  Ore  for  Sulphates.  Alkali  Wash.  Poisoning.  Potassium 
Cyanide.  Titration  of  the  Potassium  Cyanide  Solution. 

Treatment  of  Roasted  Gold  Ores  by  Means  of  Bromine.  Cyanogen 
Bromide. 

Experimental  Treatment  of  Gold-bearing  Ores.  Free-milling  Test  in 
Ball  Mill. 

Amalgamation  of  Gold  Ores.  Stamp-mill  Work.  Making  Silver 
Amalgam.  Amalgams.  Recovery  of  Silver  and  Mercury  from  the  Nitrate 
Solution. 

Bullion.  Melting  and  Refining.  Toughening.  Pouring  and  Casting.. 
Small  Amounts  of  Bullion. 

Retorting  and  Cleaning  Mercury. 

Muffle  Chloridizing  Roast  of  Silver  Ores. 

Pan  Amalgamation  of  Ores. 


OF  THE" 

UNIVERSITY 

or 


NOTES  ON  ASSAYING. 


CHAPTER  I. 
INTRODUCTION. 

APPARATUS,  REAGENTS,  AND  MATERIALS. 

ASSAYING  is  a  branch  of  analytical  chemistry  generally  defined 
as  the  quantitative  estimation  of  the  metals  in  ores,  furnace 
products,  bullion,  coin,  etc.  This  definition,  however,  makes  no- 
distinction  between  the  results  obtained  by  wet  analysis  and 
those  obtained  by  fire.  For  instance,  oftentimes  we  see  the 
expression  "assay  of  copper  ores"  or  "wet  assay  for  zinc,"  mean- 
ing the  determination  of  copper  and  zinc  by  some  well-known 
wet  method  and  not  by  fire. 

Assaying,  strictly  speaking,  is  the  quantitative  determination 
of  metals  in  ores,  furnace  products,  bullion,  etc.,  by  means  of 
fire  and  dry  reagents,  and  will  be  treated  in  this  way  in  the  follow- 
ing notes,  except  in  some  few  cases  where  a  wet  method  or  a 
combination  of  a  wet  and  a  dry  method  is  used. 

Assaying  is  chiefly  applicable  to  mining  and  metallurgical 
operations  where  we  wish  to  obtain  accurate  results  in  the  shortest 
possible  time.  An  assayer  has  generally  to  make  a  very  large 
number  of  assays  per  day;  whereas  an  equal  number  of  chemical 
determinations  would  be  out  of  the  question. 

The  student  should  realize  at  the  beginning  that  neatness, 
care,  and  thorough  attention  to  the  work  in  "hand  are  not  only 


«  NOTES  ON  ASSAYING. 

essential,  but  are  perhaps  more  important  than  in  chemical 
work.  Careful  observation  is  especially  necessary.  He  should 
also  realize  that  the  amount  of  fluxes  and  reagents,  which  make 
up  the  various  charges,  is  not  a  matter  of  guesswork,  but  each  is 
used  with  a  definite  purpose  in  view. 

Balances. — In  the  student's  laboratory  work  three  grades  of 
balances  seem  absolutely  essential;  but  one  of  these  may  perhaps 
be  dispensed  with  in  fitting  up  a  laboratory  for  himself  or  for 
some  mining  company. 

i st.  Flux-balance,  capable  of  weighing  4  kilogrammes  and 
sensitive  to  -^  of  a  gramme;  for  weighing  ore  samples,  fluxes, 
reagents,  etc. 

2d.  Pulp-balance,  balance  for  weighing  out  the  ore  to  be  as- 
sayed, lead  buttons  from  the  lead  assay,  etc.  It  should  be  sen- 
sitive to  ^  of  a  gramme,  or  2  milligrammes. 

3d.  Button-balance,  for  weighing  the  silver  beads  and  the  gold. 

This  should  be  sensitive  to  ^  of  a  milligramme.  Balances  of 
this  character  are  the  most  sensitive  and  delicate  in  the  world 
and  the  student  should  exercise  the  utmost  care  in  the  use  of 
them. 

Weights. — For  the  above  balances  we  have  four  sets  of  weights; 
but  one  of  these  may  perhaps  be  dispensed  with  in  the  ordinary 
laboratory. 

i  st.  (Flux-balance).  One  kilogramme  to  one  gramme,  for 
weighing  ore  samples,  reagents,  fluxes,  etc.  Additional  kilo- 
gramme weights  may  be  purchased  to  weigh  larger  samples. 

2d.  (Pulp-balance).  Twenty  grammes  to  one  centigramme, 
for  weighing  the  ore  for  the  lead,  copper,  and  tin  assays  and  the 
resulting  button. 

3d.  Assay,  ton  weights,  4  A.T.  to  7V  A.T.,  for  weighing  on 
the  pulp-balance  the  ores  to  be  assayed  for  silver  and  gold;  also 
base  bullion. 

4th.  Set  of  fine  weights,  one  gramme  to  one  milligramme,  to 
te  used  with  the  Button-balance. 

The  2d,  3d,  and  4th  sets  of  weights  must  never  be  handled 
with  anything  except  the  proper  pliers. 

For  these  weights  there  are  two  places,  and  only  Iwo-^vi  the 
scale- ban  or  in  the  weight-box.  If  they  are  placed  anywhere  else 


INTRODUCTION.  3 

th^y  are  liable  to  get  dust  and  other  things  on  them.  The 
s  udent,  owing  to  several  using  one  balance,  must  realize  that  not 
only  his  own  work,  but  that  of  others,  depends  upon  the  accuracy 
of  the  weights,  and  he  should  take  every  precaution  in  the  use 
and  care  of  them  accordingly. 

The  weights  formerly  used  in  assaying  were  grains,  grammes, 
or  fractions  of  these. 

Having  our  silver  or  gold  accurately  weighed,  it  was  neces- 
sary to  calculate  from  this  weight  and  the  weight  of  the  sub- 
stance taken  the  percentage  of  silver  or  gold,  and  from  this 
the  number  of  ounces  per  ton.  One  per  cent  is  equal  to  291.65 
oz.  troy  in  i  ton  avoirdupois  of  2000  Ibs. 

To  avoid  this  amount  of  calculation,  the  assay  ton  (A.T.) 
system  of  weights  was  devised  by  Prof.  C.  F.  Chandler  of  Colum- 
bia College,  N.  Y. 

All  our  ores  and  base  metals  are  weighed  in  pounds  avoirdu- 
pois; while  the  precious  metals,  gold  and  silver,  are  weighed  in 
ounces  troy. 

The  basis  of  the  A.T.  system  is  the  number  of  troy  ounces 
(29,166+ )  in  one  ton  of  2000  Ibs.  avoirdupois. 

i  ton  avoirdupois  =  2000  Ibs. 

i  Ib.  =7000  grains  troy  (i  dram  av.  =:2711/32  grains). 

Therefore 

i  ton  avoirdupois  =  14,000,000  grains  troy, 
i  oz.  troy  =480  grains. 

Therefore 

14,000,000 


480 


=  29,166+  oz.  troy. 


One  A.T.  =  29,166  milligrammes  or  29.166  grammes.  That  is, 
i  milligramme  bears  the  same  relation  to  i  A.T.  as  i  oz.  troy 
bears  to  i  ton  of  2000  Ibs.  avoirdupois,  or 

i  ton  av.  :  i  A.T.  : :  i  oz.  :  i  milligramme. 

Therefore,  as  soon  as  the  student  weighs  his  silver  or  gold, 
he  can  read  the  number  of  ounces  troy  that  his  ore  runs  per 
2000  Ibs.  avoirdupois. 


4  NOTES  ON  ASSAYING. 

Ore  Used.  Button  Obtained.  Oz.  Troy  per  Ton  Av. 

1  A.T.  .00100  grammes  I 
±A.T.  .01536        "  153.6 
JA.T.  .01220        "  24.4 

2  A.T.  .00064        "  .32 

In  Mexico,  where  the  metric  system  is  used,  the  ore  is  weighed 
in  kilograms  or  grammes  and  an  ore  is  spoken  of  as  carrying 
so  many  grammes  of  silver  or  gold  per  ton,  not  ounces  per  ton. 

Ten  grammes  of  ore  are  usually  taken  for  crucible  assay  and 
every  Vioo  'of  a  milligram  of  silver,  of  gold,  or  of  both,  equals 
the  number  of  grammes  per  metric  ton.  That  is,  if  the  silver 
from  10  grammes  of  ore  weighs  .0000 1  gramme  it  is.  equal  to- 
i  gramme  per  metric  ton  and  if  it  weighs  .00060  it  is  equal  ta 
60  grammes. 

A  metric  ton  equals  1000  kilograms. 

MEMORANDA  AS   TO   WEIGHTS   AND  VALUES. 

i  gramme       =     15.432  grains, 
i  ounce  av.    =  437 \  "       =  28.34  grammes, 

i      "      troy  =  480  "       =31.11  '   " 

i  pound  av.    =  7000  "      troy. 

The  ounce  and  pound  in  troy  and  apothecary  weights  are 
the  same. 

One  ounce  of  gold  is  worth  $2067/100. 

One  dollar  gold  coin  weighs 25.8    grains  troy 

Ten  per  cent  is  alloy  (copper) 2.58     " 

Gold : 23.22     "         "    or  $I.OQ 

480  grains  =  i  oz.  troy. 

.*.  -     —  =20.67  or  $2067/100  per  oz.  troy. 

$800  in  gold  weigh  43.00  oz.  troy. 

/.  ^X43  or  38-7  oz.  troy  is  gold. 
.*.  i  ounce  troy  =  $2O67/100. 


INTRODUCTION  5 

One  silver  dollar  (by  law  of  U.  S.  90  parts  silver,  10  parts 
topper)  weighs  412 \  grains.  $i280/10o  in  silver  coin  weigh  n  oz. 
troy,  or  i  oz.  is  worth  $i29/ioo  +  -  $1.29+  Xi6  =  $2O67/ioo;  hence 
the  ratio  in  coinage  of  16  to  i. 

A  fifty-cent  silver  piece  weighs  12.5  grammes  or  192. 9  grains. 

i  Ib.  troy  =  5  760  grains. 

.*.  2000  fifty-cent  pieces  weigh  66.9  Ibs.  troy  or  55.1  Ibs.  av. 

Sterling  silver  should  contain  925  parts  of  silver  in  1000. 
The  remainder  consists  of  copper  and  a  small  percentage  of 
some  metal  like  cadmium,  which  makes  it  roll  more  readily. 

One  ton  of  gold  is  worth  29,166  oz.  X$2O.67,  or  $602,861.22. 

$20.67 

One  gramme  of  gold  is  worth  -       —  =  66  cents. 

31.11 

One  grain  of  gold  is  worth  43/io  cents. 

When  we  speak  of  gold  we  often  refer  to  it  as  so  many  carats 
fine.  In  this  case  we  mean  parts  in  24;  that  is,  if  a  ring  is  22 
carats,  it  means  that  22  parts  in  24  are  gold,  and  the  other  two 
parts  alloy  of  either  silver,  copper,  or  both  silver  and  copper. 

An  ordinary  carat  =  205  milligrammes  or  31/,,  grains  troy,  i.e., 
151.76  carats  =  i  troy  oz.  Jewelers  divide  this  carat  into  4  grains, 
called  diamond-grains  or  carat-grains. 


ASSAY  REAGENTS. 
The  reagents  used  in  assaying  may  be  divided  as  follows: 

i  st.  Reducing  agents. 

2d.  Oxidizing  agents. 

3d.  Desulphurizing  agents. 

4th.  Sulphurizing  agents. 

5th.  Fluxes. 

ist.  Reducing  Agents.  —  When  a  metal  is  separated  from 
a  state  of  chemical  combination  it  is  said  to  be  " reduced,"  and 
the  process  of  separation  is  termed  "reduction."  (Percy.) 


o  NOTES  ON  ASSAYING. 

The  agent  by  which  the  reduction  is  effected  is  termed  a 
"reducing  agent."  (Percy.) 

2PbO+C=2Pb+CO2. 
Here  the  carbon  is  the  reducing  agent. 

PbS+Fe=Pb+FeS. 

In  this  reaction  the  iron  reduces  metallic  lead;  but  we  generally 
speak  of  the  iron  as  a  desulphurizing  agent,  f- 

A  reducing  agent  is  also  denned  as  a  substance  which  is  capable 
of  taking  away  oxygen  from  those  compounds  with  which  it  is 
combined  and  which  are  willing  to  part  with  it. 

Chemically,  it  is  defined  as  a  compound  or  element  which 
takes  away  an  acid  radical  and  gives  up  a  basic  one. 

The  following  are  the  reducing  agents  most  commonly  used  : 

Charcoal.—  From    the    reaction    2PbO+C  =2Pb+CO2,    this 


should  have,  if  pure,  a  reducing  power  of  -        —  =  34  J  grammes 

of  lead.  But  as  used  it  is  seldom  pure,  and  it  has  a  reducing 
power  of  only  24  to  28  grammes. 

Argols.  —  Reducing  power  of  7  to  u,  depending  upon  the 
purity. 

Cream  of  Tartar.  —  Reducing  power  about  5  grammes. 

Potassium  Cyanide. 

Flour.  —  Reducing  power  about  11.9  grammes. 

Starch.—      "  "          "       12 

Rosin. 

2d.  Oxidizing  Agents.  —  These  give  up  oxygen  easily. 

Oxygen  of  the  air:  2FeS2-f-nO  =4SO2+Fe2O3. 

Litharge:  PbO  +  Fe  =  FeO+Pb. 
2PbO+S  =  SO2+2Pb. 

Ferric  oxide  (Fe2O3)  and  Manganese  binoxide  (MnO2).  —  In 
the  presence  of  carbon  these  are  both  reduced  to  protoxides: 
Fe2O3+  C  =  2FeO  +  CO.  (See  page  72  .  ) 


INTRODUCTION.  7 

Nitrates  of  Potassium  and  Sodium.  —  These  are  most  power- 
ful oxidizing  agents;  and  if  in  the  presence  of  sulphides  an 
excess  is  used,  H2SO4  is  formed.  On  sulphides  of  Ag,  Cu,  and 
Pb,  that  is,  sulphides  not  easily  oxidized,  the  nitre,  if  used  in 
exact  quantity,  will  leave  the  metals  pure,  and  oxidize  the  sulphur 
to  H2SO4  or  SO3  or  both.  On  other  sulphides  it  not  only  forms 
SO3,  but  also  the  oxides  of  the  metals: 

4ZnS+  6KNO3  =  4ZnO  -f  3K2SO4+  SO2+  6N. 

A  substance  is  oxidized  when  oxygen  or  some  other  acid  ele- 
ment or  radical  is  added  to  it;  or  when  hydrogen  or  a  basic  ele- 
ment is  taken  from  it.  For  the  determination  of  the  oxidizing 
power,  see  page  81. 

Alkaline  Carbonates.  —  These  owe  their  oxidizing  power  to  the 
CO2  contained  and  given  off  upon  heating: 


3d.  Desulphurizing  Agents. 
Oxygen:  2FeS2+  i  lO  =  Fe2O3+  4SO2. 

Charcoal.—  Forming   sulphide   of   carbon   and   reducing   sul 
phates  to  sulphides:  FeSO4+3C=FeS+2CO+CO2. 
Iron:  PbS+Fe  =  FeS+Pb. 
Alkaline  Carbonates: 

4K2C03+  yPbS  =  4Pb+3(K2S,PbS)  +  K2S04+4C02. 


Litharge:       PbS-f  2PbO  =  SO2 

2FeS2+  uPbO  =Fe2O3+4SO2+  uPb, 
or  FeS2+  sPbO  =  FeO+  2SO2-f  $Pb. 


Litharge  decomposes  all  sulphides  in  this  way,  and  in  so  doing 
lead  is  reduced  and  we  find  that 

i  gramme  of  pyrite  will  reduce  about  10  grammes  of  lead. 
i         "        "  blende     "        "          "       9         "        "    " 
i         "        "  galenite  will  reduce  about  2\       "        "    " 


3  NOTES  ON  ASSAYING. 

Nitre.  —  This  acts  under  heat  as  follows: 


2KNO3=K2O  +  N2O5;  N2O5 

6KNO3+  2FeS2  «  3K2SO4  +  SO3+  Fe2O3+  6N. 

4th.  Sulphurizing  Agents. 

Sulphur. 

Sulphides,  such  as  iron  pyrites  and  galenite. 

5th.  Fluxes.  —  A  flux  is  something  which,  if  added  to  a  body 
infusible  by  itself  or  with  difficulty  fusible,  will  cause  it  to  fuse. 
For  instance,  take  some  quartz  carrying  free  r>;old,  the  amount  of 
which  we  wish  to  determine.  In  order  to  melt  the  quartz,  which 
is  acid,  we  shall  have  to  heat  it  far  above  1064°  C.,  the  melting- 
point  of  gold.  Still  the  gold  will  not  entirely  separate.  If,  how- 
ever, we  add  some  Na2CO3,  a  basic  flux,  to  the  ground  quartz,  we 
•shall  form  a  fusible  silicate  of  soda,  and  the  gold,  owing  to  its 
Mgh  specific  gravity,  will  then  separate  out  easily. 

The  sodium  carbonate  is  the  flux  added: 

Na2CO3+  SiO2  =  Na2SiO3+  CO2, 
•and  the  sodium  silicate  is  the  slag  formed  during  the  fusion. 

To  determine  what  flux  or  fluxes  to  add  to  any  ore  or  material, 
the  student  should  remember  that  if  the  ore  is  basic,  like  lime- 
•stone  or  iron  oxide,  it  will  require  a  flux  which  acts  as  an  acid, 
like  silica  or  borax.  If  the  ore  is  acid,  it  will  require  a  flux  which 
acts  as  a  base,  like  iron  oxide,  limestone,  or  litharge. 

The  following  are  the  principal  fluxes  used  in  assaying: 

Litharge  Borax  Nitre 

Lead  Borax  glass  Limestone 

Na2CO3  or  NaHCO3    Silica  Fluorspar 

K2CO3  Argols      )  Iron  oxide 

Charcoal  [  KCN 

Flour       / 


INTRODUCTION.  9 

FUSION  PRODUCTS. 

In  all  the  fusions  he  makes,  whether  by  scorification  or  by  cru- 
cible, the  student  should  obtain  a  button  of  some  of  the  metals, 
a  slag,  and  possibly  a  matte  or  a  speiss  besides. 

Slag. — This  is  the  refuse  or  waste  material  from  the  ore  or 
substance  worked  upon.  Slags  are  either  acid  or  basic.  An 
acid  slag  tends  to  be  glassy  and  brittle,  and  when  melted  can  be 
pulled  out  into  long  strings  like  molasses  candy.  If  the  slag  is 
basic,  it  is  dull  and  stony- looking;  it  is  tough  when  cold  and  can- 
not be  pulled  out  into  strings  when  melted  or  near  the  chilling- 
point. 

The  fusibility  of  slags  varies  a  great  deal.  As  a  rule  the 
combination  of  several  substances  makes  a  more  fusible  mix- 
ture or  slag  than  a  combination  of  only  two.  The  slags  from 
lead  and  copper  smelters  are  essentially  silicates  of  iron  and 
lime  or  iron,  alumina,  and  lime;  those  from  an  iron  furnace  are 
silicates  of  lime,  magnesia,  and  alumina. 

In  our  assay  work  this  question  of  fusibility  must  be  con- 
stantly borne  in  mind.  We  are  forming  silicates  of  soda  or  lead 
or  a  combination  of  these  with  various  oxides  and  borates,  and 
although  many  silicates  are  very  fusible  others  are  quite  infusible. 
A  fusion  may  therefore  be  perfectly  liquid  in  a  pot  furnace  and 
yet  thick  and  full  of  shots  of  lead  in  a  muffle  furnace,  where  the 
heat  is  not  so  high. 

Slags  should  be  homogeneous  and  contain  no  streaks  or  parti- 
cles of  substance  that  are  apparently  undecomposed.  They  vary 
in  color,  depending  upon  the  fluxes  used  and  the  ingredients  in 
the  ore  or  substance.  A  red  slag  indicates  copper  oxide  (Cu2O) ; 
a  very  light  green  indicates  a  ferrous  silicate.  At  times  the  color 
seems  to  depend  upon  the  temperature  at  which  the  fusion  was 
conducted. 

The  four  following  fusions  made  at  one  time  will  serve  as  an 
example 


10 


NOTES  ON  ASSAYING. 


ORE    NO.    1551. 
A  silicious  ore  carrying  a  little  iron  oxide  and  a  small  amount  of  pyrite. 


i.* 

2  A.f 

aB.J 

3.§ 

Ore                

i  A.T. 

i  A.T. 

i  AT 

2  A  T 

Sodium  bicarb    grammes               .    . 

60 

en 

80 

Borax                        "                  ... 

5" 

ou 

:>u 

5 

Litharge                     " 

CQ 

Cn 

P.O 

*7O 

Ar^ols                         " 

ou 

•     , 

Salt  

cover 

cover 

cover 

cover 

Weight  of  Pb  button                   

20 

20 

a* 

\Veight  Ag  and  Au                      .... 

02  Too 

028015 

02825 

o4 
QC  COC 

Correction  for  the  Ag  in  the  PbO  used  . 
Weight  Au                    

.00051 
00271; 

.00051 
00263 

.00051 
00^70 

•V^3V> 

.00072 
00526 

2  A    6/1 

2  A     QT 

2C.    O4. 

2A    8^ 

Ounces  per  ton  Au  

2    7C 

2.  6-? 

2    7O 

2  6-? 

*  Fused  55  min.  at  bright  heat.     Slag,  dark  gray,  stony,  homogeneous,  opaque. 

t  Fused  55  min.  at  bright  heat.  Slag,  dark  gray,  streaked  with  black,  somewhat 
glassy,  opaque. 

J  Fused  ss  min.  at  much  lower  heat.  Slag,  green,  stony,  homogeneous,  translucent  ort 
edges. 

§  Fused  55  min.  at  bright  heat.  Slag,  dark  green,  streaked  with  black,  somewhat 
glassy  and  translucent  on  edges. 

The  specific  gravity  of  a  slag  must  also  be  taken  into  con- 
sideration, for  if  it  is  too  high  the  metal  to  be  recovered  will 
not  readily  settle  out. 

All  slags  obtained  from  any  work  should  be  kept  in  the  proper 
trays  on  the  iron  table,  for  they  will  soon  destroy  the  furnace- 
linings  if  they  get  mixed  with  the  fuel. 

The  student  may  also  meet  with  the  following : 
Matte   or  Regulus. — These  terms  have  the  same  meaning. 
The  former  is  generally  used  in  this  country,  and  the  latter  abroad. 
They  are  applied  to  a  metallic  sulphide,  formed  by  the  com- 
bination of  the  metal  with  sulphur  at  an  elevated  temperature. 
Copper  matte  =  2Cu-f  S  =  Cu2S; 
Iron  matte      =  Fe  +S  =  FeS; 
Lead  matte     =  Pb  -f  S  =  PbS. 

Speiss  or  Speise. — This  term  is  applied  to  a  metallic  arsenide 
or  antimonide  formed  in  smelting  operations,  so  we  speak  of  a 
nickel-cobalt  speiss  or  an  iron  speiss. 

Examples : 


Nickel 


s  = 


Iron  Speiss  =Fe5As,  containing  21.12%  As. 


INTRODUCTION.  n 

If  we  use  iron  in  assaying  an  ore  containing  arsenic,  we  often 
speiss.  Hard  and  brim*       find  as  the  result  of  the  fusion  a  lead 

d.  Soft  and  arable.          ^^    and    a    speiss    lying    aboye    ft    thus  . 

A  high  temperature  and  a  small  amount  of  alkaline  flux  tend 
to  the  formation  of  an  iron  speiss  (see  assay  of  gold  ores,  p?ge  137)  ^ 

If  metal,  speiss,  matte,  and  slag  were  all 
present  in  one  fusion,  they  would  separate  out 
in  the  order  given  in  the  accompanying  figure. 

It  seems  rather  doubtful  in  what  condition 
the  antimony  and  arsenic  exist  in  a  speiss. 
It  is  generally  true  that  as  the  antimony  and 
the  arsenic  increase  in  amount,  the  specific 
gravity  of  the  speiss  also  increases. 

-FURNACES   AND   FUELS. 

In  our  assay  work  we  make  use  of  two  kinds  of  furnaces, 
the  mufrle  and  the  crucible  furnace.  In  the  latter  our  assay 
vessels  are  in  direct  contact  with  the  fire,  while  in  the  former  they 
are  not.  These  furnaces  may  be  heated  with  solid,  liquid,  or 
gaseous  fuel,  the  choice  and  use  depending  partly  upon  price, 
and  partly  upon  locality. 

Crucible  fusions  can  also  be  made  in  a  muffle,  and  some  fur- 
naces are  built  in  combination. 

Our  solid  fuel  consists  of  charcoal,  coke,  anthracite,  and  bitu- 
minous coal.  Any  of  these  may  be  used  in  heating  a  muffle-furnace, 
the  first  three  heating  it  by  actual  contact,  the  last  by  its  flame 
alone.  All,  with  the  exception  of  the  bituminous  coal,  can  be 
used  for  the  crucible-furnace.  Gaseous  and  liquid  fuels  may  be 
used  in  either  furnace. 

In  using  solid  fuel  the  furnace  has  to  be  constantly  fed; 
whereas  in  using  gaseous  or  liquid  fuel  the  supply  can  be  regulated 
and  the  heat  much  better  adjusted. 

The  furnaces  themselves  may  be  made  of  bricks  or  tiles  alone 
and  then  hooped  with  iron,  or  an  iron  shell  may  be  made  of  the 
desired  shape  and  size  and  then  lined  with  fire-brick  on  the 
inside.  These  bricks  should  fit  very  closely  together,  and  the 
least  practical  amount  of  fire-clay  mortar  should  be  used.  The 


12  NOTES  ON  ASSAYING. 

brick  and  tile  furnaces,  hooped  with  iron,  are  certain  to  crack, 
owing  to  the  constant  expansion  and  contraction. 

REFRACTORIES. 

Fire-clays. — Fire-clays  are  practically  silicates  of  alumina, 
and  are  so  named  on  account  of  their  ability  to  resist  high  tem- 
peratures without  softening.  They  are  also  called  refractory 
•clays.  Their  plasticity  depends  upon  their  water  of  combination : 

2Al203,3Si02;  Al203,2Si02+  H2O. 

'Their  shrinkage  is  from  2^  to  5  per  cent. 

The  impurities  most  commonly  found  in  clays  are  oxide  of 
iron,  carbonate  of  lime,  and  the  alkalies.  These  all  tend. to  make 
the  clay  fusible,  as  they  combine  with  the  silica  present  in  the  clay. 

The  nearer  we  can  have  the  clay  to  a  simple  combination  of 
SiO2  and  A12O3  the  better  it  seems  to  be;  and  the  larger  the  pro- 
portion of  SiO2  the  more  refractory  it  is. 

Percy  gives  the  following  analyses  of  clays: 


us 
SiO 

Stourbridge  Clay,              •R0irr;1,n              Dowlais, 
ed  for  Glass-pots.              Belgium.       South  Waleg 

63.3%                           57-12%          67.12% 
23.3%                           29.06%          21.18% 
•73%                                -04%                -32% 
1.8%            Fe203     .45%           1-85% 

10.30%                        9-3°% 
MgO     .70%             .84% 
Alkalies  1.14%           2.02% 
H2O  of  combination  4.  82% 

Kaoline. 

53-7% 
44-3% 
Trace. 

•9% 

Trace 
K20     1.2% 
Na20  

A1O 

23' 

CaO 

FeO   

H2O  and  organic 
matter     .    .    • 

Hydroscopic  water    i .  39% 

V 

Some  authorities  go  so  far  as  to  say  that  a  small  amount  of 
alkalies  is  rather  beneficial,  as  they  act  as  a  sort  of  cement  to 
the  material. 

Fire-brick. — These  are  made  from  refractory  clays  and  vary 
not  only  in  composition  but  in  the  texture  of  material.  Some 
bricks  are  very  coarse-grained  and  some  very  fine,  depending 
upon  where  they  are  to  be  used.  They  fuse  at  between  1400° 
and  i7oo°C.  Prof.  C.  L.  Norton  of  the  Institute  of  Technology 
found  that  some  fu.  ed  at  between  1600°  and  1700°  C. 


INTRODUCTION. 


FURNACES  USED   IN   THE  LABORATORY  AT  THE  MASSACHUSETTS 
INSTITUTE   OF  TECHNOLOGY. 


Sliding  cover 

with  9$"iron 

-K"lron  plate 
Flue  4  M"x  3" 


Iron  shell  H 
Fire  brick.  4" 

A.  Grate  bars  &"x 

™  2  J/ fire  brick 
--  Redbrick 


10  Air  space 

CRUCIBLE  FURNACE 


This  will  hold  six  E  or  F,  five  G  or  H,  or  two  Ks. 


Flue  l"x.  7  Opening  to  flue.  Draft 
_  partly  regulated  by  loose  brick 


flron  shell  Alined  with  4^  of  fire 
J     brick,back  and  sldes,and7" 
in  front 

-  Feed  door  for  fuel 
Muffle  CK.L  or  L  L) 


Stoking  door 
-Grate  bars,  l"sq.  x  14' 


MUFFLE  FURNACE 
It  will  hold  4  E,  F,  G,  or  II  crucibles,  or  2  K  or  2  L. 


NOTES   ON  ASSAYING. 


Scorifier-tongs.  * 


Muffle. 


Crucible-tongs. 


MUFFLE- FURNACE  ( Judson) . 

b  =  stoking-door.     In  small  furnaces  sometimes  it  is  at  a. 

c  =  ash-pit. 

d=  muffle. 

e  =  where  fuel  is  charged. 


*  See  excellent  paper  by  Mr.  Edward  Keller  on  Labor-saving  Appliances  in 
the  Works- Laboratory,  A.  I.  M.  E.,  February,  1905. 


INTRODUCTION.  *5 

Crucibles. — Crucibles  are  made  from  prepared  clays,  or  from 
suitable  mixtures,  in  either  of  two  ways : 

i st.  By  moulding  upon  a  potter's  wheel. 

2d.  By  compressing  the  clay  or  mixture  into  moulds  of  the 
•desired  form. 

Crucibles  should  have  the  following  properties: 

1.  They  should  be  infusible. 

2.  They  should    be    able  to  withstand  sudden  changes  of 
temperature. 

3.  They  should  be  only  slightly  acted  upon,  not  only  by  the 
charge  within,  but  by  the  ashes  from  the  fuel  without. 

4.  They  should  be  as  much  as  possible  impermeable  to  the 
.substances  fused  in  them,  and  also  to  gases. 

The  most  infusible  crucibles  are  made  from  clays  having  a 
high  percentage  of  SiO2  and  carrying  only  small  amounts  of  iron 
oxide,  lime,  and  the  alkalies. 

Lime,  magnesia,  and  alumina  crucibles  are  made  and  are 
extremely  infusible,  but  they  are  used  only  for  special  purposes. 

The  infusibility,  as  well  as  the  power  to  withstand  sudden 
changes  of  temperature,  is  increased  by  adding  some  substance 
like  quartz,  graphite,  coke,  and  ground  flints  to  the  clay.  These 
substances  neither  expand  nor  contract  and  they  make  a  sort  of 
infusible  framework  for  the  rest  of  the  material.  Old  crucibles 
or  old  glass-pots,  with  the  vitrified  matter  carefully  chipped  off, 
are  sometimes  used.  Crucibles  that  are  dense  and  close-grained 
are  the  least  acted  upon  by  the  fusion,  i.e.,  the  material  must  be 
finely  ground  and  not  coarse.  This  is  the  reason  why  a  crucible 
like  the  Beaufay  is  so  much  superior  to  a  Hessian. 

Crucibles  are  tested,  as  regards  their  resistance  to  oxides,  by 
fusing  litharge  (PbO)  in  them  and  noting  the  time  it  takes  the 
litharge  to  eat  through. 

Filling  the  crucible  with  water  and  noticing  the  time  it  takes 
to  make  the  crucible  moist  upon  the  outside  is  a  test  as  to  its 
permeability  to  liquids. 

A  clay  crucible  should  not  be  placed  directly  upon  hot  coals. 
It  will  crackle  audibly  and  later  on  it  may  crack.  Always  put 


1 6  NOTES  ON  ASSAYING. 

some  cold  fuel  upon  the  fire  and  then  place  the  crucible  or  cru- 
cibles upon  that. 

Berthier  gives  the  following  analyses  of  crucibles : 

SiO2.  A12O3.          Fe2O3         MgO         K2O. 

Per  Cent.      Per  Cent.    Per  Cent.  Per  Cent.  Per  Cent. 
Hessian 70.90         24.80        3.80  Made  of  clay  and  sand. 

English 71.00         23.00         4.00  \  Used  for  melting  steeL 

(      Probably  clay  alone. 
St.  Etienne..    65.20         25.00         7.20  Used  for  melting  steeL 

Bohemian 68.00         29.00        2.20         .50  Used  for  melting  glass. 

Cornish 72.39         25.32         1.07          .38         1.14 

Beaufay 64.60         34.40         i.oo 

Crucibles  are  used  both  in  the  burnt  and  the  unburnt  condition. 
Small  crucibles  are  generally  kiln-burnt.  The  large  clay  pots 
made  at  Stourbridge,  England,  and  used  largely  by  brass-founders 
are  never  burnt,  but  are  slowly  dried  and  then  heated  very  carefully,. 
as  a  graphite  crucible  would  be  when  placed  in  the  furnace. 

Oftentimes  it  is  necessary  to  give  crucibles  a  coating  of  some 
substance  that  will  prevent  absorption  by  the  crucible  and  yet  be 
harmless  to  the  fusion.  Silver  chloride,  for  instance,  will  very 
quickly  soak  into  the  pores  of  a  crucible.  To  prevent  this,  take  the 
new  crucible  and  fill  it  with  a  boiling  saturated  solution  of  borax, 
allow  to  stand  for  some  minutes  and  then  pour  out.  Set  crucible 
aside  to  dry.  Borax  and  borax  glass  may  also  be  melted  in  the 
crucible,  and  then  swashed  around  until  the  inside  is  glazed  over. 
This  glaze  not  only  prevents  substances  soaking  into  the  crucible,. 
but  acts  as  a  glaze  of  salt  would,  and  prevents  any  metallic  par- 
ticles adhering  to  the  sides  of  the  crucible. 

When  a  crucible  does  not  crack,  is  only  slightly  corroded, 
and  is  clean  from  a  previous  fusion  it  may  be  used  again.  The 
amount  of  corrosion  depends  partly  upon  the  character  of  the 
charge  and  partly  on  the  temperature  of  the  fusion.  With  a 
silicious  charge  an  ordinary  crucible  will  be  only  slightly  attacked, 
while  if  the  litharge  is  high  and  the  charge  basic  the  corrosion 
will  be  very  marked.  A  basic  crucible,  on  the  other  hand,  will 
be  attacked  by  a  silicious  charge. 

The  size  of  most  crucibles  is  indicated  by  letters  or  numbers, 
stamped  on  the  side  or  bottom.  The  larger  the  number  or  the 


INTRODUCTION.  X7 

higher  the  letter  in  the  alphabet,  the  larger  the  crucible.  Any 
number  may  be  purchased.  Original  casks  of  Battersea  cru- 
cibles contain,  of  A's,  1800;  of  F's  (5"  highX3"  diam.),  500;  of 
G's  (5f"X3J"),  400,  and  of  H's  (5J"X3|"),  3°°- 

The  sizes  of  Hessian  crucibles,  triangular  and  round,  are 
designated  as  3%  Small  s's,  Centimetres,  Large  s's,  Sixes,  Eighths, 
Halves,  Ones,  and  Double  Extras. 

Covers  are  sold  to  fit  all  sizes  of  crucibles. 

GRAPHITE   CRUCIBLES. 

Graphite  is  pure  carbon  when  the  mineral  itself  contains  no 
impurities.  It  may  occur  massive,  earthy,  or  crystalline,  and  is 
often  found  in  scales  and  grains  in  granite,  limestone,  and  slate. 
The  principal  sources  of  supply  are  Ceylon,  Russia,  Mexico,  and 
Ticonderoga,  N.  Y. 

Pure  graphite  neither  melts,  softens,  nor  changes  in  any  way 
when  heated  to  very  high  temperatures,  provided  oxygen  is  ex- 
cluded. It  burns  very  slowly  when  heated  in  the  air. 

Percy  gives  the  following  as  analyses  of  some  samples  of 
graphite: 


(Si02  52.5%;  A1203  28.3%; 
\  FeO  12%;  CaO  and 
(  MgO=6% 


Sp.Gr.  Vol.  Matter.  Carbon.           Ash. 

English...     2.34  1.10%     91 .55%  7-35% 

English...  86.7%  13.3%         Used  for  pencils. 

Ceylon....  96.1%  3.9% 

Russian...     2.17  .72%     94.03%  5-25% 


As  graphite  is  not  plastic,  it  is  mixed  with  fire-clay  and  then 
moulded.  The  proportions  are  generally  one  part  fire-clay  and 
three  parts  graphite,  the  clay  acting  as  a  frame  for  the  crucibles. 
They  withstand  extremely  high  heat  and  sudden  changes  of  tem- 
perature. Oxides,  when  fused  in  them,  are  reduced  to  the  metallic 
state  and  soon  consume  the  graphite  in  the  crucible.  This, 
together  with  the  gradual  consumption  of  the  carbon  upon  the 
outside  of  the  crucible,  eventually  destroys  them.  Before  using 
they  should  be  kept  in  a  dry  place  and  annealed  right  side  up 
at  about  250°  to  300°  Fah.  until  free  of  moisture.  When  first 


T8  NOTES  ON  ASSAYING. 

lieated,  it  is  safer  to  place  them  in  the  fire  in  an  inverted  position, 
otherwise  they  are  liable  to  crack  and  sometimes  to  explode. 
When  red  all  through  they  are  turned  right  side  up  and  are 
then  ready  to  receive  the  charge.  In  crucible- steel  works  it  is  not 
possible  to  do  this  owing  to  the  crucible  being  full  when  placed 
ui  the  furnace,  but  there  is  always  a  deep  layer  of  unburnt  fuel 
beneath  them  when  used. 

The  first  fusion  should  be  made  as  rapidly  as  possible  con- 
sistent with  the  safety  of  the  pot,  so  as  to  glaze  both 
outside  and  inside  by  melting  the  binding  material. 
The  tongs  for  lifting  them  should  fit  just  below 
the  bulge  of  the  crucible.  This  avoids  any  danger 
•of  undue  squeezing  and  consequently  cracking. 

Although  the  crucibles  are  all  carefully  made,  there  seems  to 
be  a  great  difference  in  those  of  one  lot  of  the  same  grade 
and  intended  for  the  same  purpose.  The  material  to  be  fused 
in  them  determines  their  composition  and  the  manner  of  treat- 
ment during  their  manufacture.  A  crucible  may  stand  from  one 
to  thirty  or  more  fusions,  depending  upon  the  manner  of  their 
handling  and  the  substance  fused  in  them. 

The  texture  of  the  graphite  and  the  kind  of  fire-clay  employed 
has  a  great  deal  to  do  with  this,  as  well  as  the  manner  of  baking 
•and  firing.     (See  Iron  Age,  May  20,  1897,  paper  by  John  A. 
Walker.) 

The  Jos.  Dixon  Crucible  Co.  (mines  at  Ticonderoga,  N.  Y., 
and  works  at  Jersey  City,  N.  J.),  in  making  their  crucibles,  use 
about  50%  graphite,  17%  sand,  and  33%  fire-clay  (air-dried). 
They  have  also  twenty  or  more  other  formulas,  according  to  the 
~use  to  which  the  crucible  is  to  be  put.  The  fibrous  variety  of 
graphite  is  preferred,  because  its  binding  properties  are  greater. 

The  graphite  must  pass  a  4o-mesh  screen;  if  it  is  ground  too 
fine,  the  crucible  will  be  too  dense;  if  too  coarse,  the  crucible 
will  be  too  porous. 

The  sand  must  also  pass  a  4o-mesh  screen. 

Manufacture. — Formerly  the  clay  was  made  into  a  thin  paste 
with  water  and  the  sand  and  graphite  next  mixed  in  and 
passed  two  or  three  times  through  a  pug-mill.  The  ingredients 


INTRODUCTION.  19 

are  to-day  thoroughly  mixed  and  kneaded  in  a  machine  with 
revolving  knives  and  then  tempered  several  weeks  in  a  damp 
place  or  kept  covered  with  damp  cloths.  Weighed  lumps  of 
the  tempered  material  are  next  kneaded  and  then  moulded 
on  a  wheel,  or  else  the  kneaded  dough  is  put  into  a  plaster- 
of-Paris  mould,  which  it  only  partly  fills,  and  rammed  in  hard. 
The  mould  is  now  put  in  an  iron  holder  and  set  revolving, 
while  a  plunger  is  gradually  lowered  at  one  side  into  the  mould. 
By  its  action  the  dough  now  gradually  rises  up  to  the  top  of 
the  mould  and  we  have  a  crucible  inside  a  plaster-of-Paris  mould. 
This  method  of  manufacture  tends  to  place  the  graphite  flake 
tangentially.  The  crucibles  are  allowed  to  stand  in  the  moulds 
several  days,  during  which  time  part  of  their  water  is  absorbed. 
They  are  then  removed,  finished,  or  smoothed  on  the  outside  and 
dried  for  a  week  or  more  at  70°  to  80°  Fah.  Finally  they  are 
burned  in  a  pottery- kiln,  heated  by  anthracite  or  a  long- flaming 
wood.  The  temperature  is  1100°  to  1300°  Fah.,  and  the  flame 
does  not  touch  the  crucibles. 

Graphite  crucibles  are  numbered  from  oo  upward,  and  up 
to  about  No.  1 6  cost  so  much  per  crucible;  beyond  this  they 
cost  so  many  cents  per  number  and  are  supposed  to  hold  3  Ibs. 
of  metal  per  number. 

Scorifiers. — These  are  the  vessels  in  which  the  scorification 
process  is  carried  on  in  the  muffle.  They  are  made  of  refrac- 
tory clay  which  is  more  finely  ground  than  that  used  in  the  manu- 


facture  of  most  crucibles.  One  man,  in  eight  hours,  can  make 
about  1000  of  them,  and  they  would  weigh  from  150  to  250  Ibs. 
The  principal  foreign  makes  are  the  Battersea  (English),  Beau- 
fay,  and  Freiberg.  The  forms  are  either  deep  or  shallow.  The 
sizes  are  i",  ij",  i}",  2",  a*",  aj",  af,  3",  3i",  4",  and  5" 
diam.,  outside  measurement. 

Original  casks  hold  2700  of  2^"  diam.,  1600  of  3",  and  650 
of  4". 


20  NOTES   ON  ASSAYING. 

Scorifiers  may  be  used  more  than  once,  but  as  they  are  very 
cheap  it  hardly  pays  to  run  the  risk  of  their  being  eaten  through 
the  second  time  they  are  used  and  thus  losing  an  assay.  If  the 
inner  surface  is  rough  and  much  corroded  no  attempt  to  use  them 
a  second  time  should  be  made.  When  scorifying  a  lead  button> 
to  diminish  it  in  size  or  to  oxidize  the  impurities  present  and  to 
slag  them  off,  a  small  amount  of  silica  (SiO2)  should  always  be 
added  after  the  lead  button  has  jused  and  commenced  to  "  drive." 
The  PbO  combines  with  this,  and  by  so  doing  the  scorifier  is  not 
so  much  attacked  and  eaten  into. 

Cupels. — These  are  used  for  the  cupellation  of  lead  buttons 
containing  silver  and  gold.  They  are  made  from  the  bones  of 
horses  or  sheep  and  have  the  property  of  absorbing  the  oxides 
of  the  base  metals,  leaving  the  gold  and  silver.  The  bones  are 
burned  until  they  are  perfectly  white,  leaving  from  60%  to  70% 
ash,  and  are  then  ground  so  fine  that  they  will  pass  a  40-  to  60- 
mesh  sieve.  The  bone-ash  is  then  ready  for  use  and  consists- 
chiefly  of  calcium  phosphate  ^CaO^Os),  with  some  calcium 
oxide  (CaO).  The  bones  of  oxen,  according  to  Bloxam,  analyze 
before  burning  as  follows: 

Animal  matter 30 . 58% 

Calcium  phosphate 57 . 67% 

"        fluoride.  , 2 . 69% 

' '        carbonate 6 . 99% 

Magnesium     "       2 . 07% 

The  ash  from  the  burned  bones  would  then  analyze  about  as 
follows : 

Calcium  phosphate 88 . 00% 

* '  fluoride 4 . 10% 

"  oxide 6.39% 

Magnesium  oxide i  •  5 1% 

The  following  will  give  some  idea  of  the  bone- ash  on  the 
market  as  passing  a  4o-mesh  sieve: 

ist  Barrel.  2d  Barrel. 

On  4o-mesh  sieve 5  %  .  9% 

Through  40  on  60  sieve 3.00%  26. 2% 

60  "  80     "     i5-9°%  )  19-2% 

"        80  "   100  "    27.8o%U6.5o%  2i.8% 

"        100  sieve 52.8%    )  32.1% 


INTRODUCTION. 


21 


The  cupels  are  made  by  moistening  the  bone-ash  with  water 
alone,  or  with  any  one  of  the  following  solutions :  pearl  ash, 
borax  (i%  to  2%)  in  H2O,  Lour  beer  or  molasses  (i%  103%) 
in  H2O.  Some  prefer  one,  some  another.  It  is  made  just 
moist  enough  to  stick  together  when  pressed  in  the  hand,  and 
the  cupels  must  come  out  of  the  moulds  easily. 

10  to  24  per  cent  of  water  will  suffice,  depending  upon  the 
freshness  and  the  quality  of  the  bone-ash.  A  less  percentage  will 
be  required  if  a  binding  substance  like  molasses  is  added  to  the 
water. 

It  is  then  ready  to  compress  in  the  cupel  moulds  of  any  desired 
size,  either  by  hand  or  by  machine.  The  size  and  shape  of  the 
cupel  varies  as  well  as  that  of  the  bowl.  The  cross-sections, 


actual  size,  of  two  used  in  this  laboratory  are  given.  The  com- 
pressing, if  done  by  hand,  is  a  matter  of  practice.  Some  assayers 
prefer  to  make  the  bottom  layer  of  a  cupel  of  40-mesh  material 
and  then  put  a  finer  layer  on  top,  compressing  all  at  once.  If 
too  much  compression  is  used,  the  cupels  will  be  too  hard,  the 
litharge  (PbO)  will  be  very  slowly  absorbed,  prolonging  the 
cupellation  and  resulting  in  the  loss  of  precious  metals. 

If  too  soft,  they  are  fragile  and  the  litharge  will  be  apt  to 
•carry  the  precious  metals  with  it  into  the  cupel. 

One  kilogram  of  bone-ash  will  make  from  25  to  32  cupels,  in 
which  a  lead  button  can  be  cupelled  weighing  from  25  to  30 
grammes. 

They  should  be  well  dried,  preferably  air-dried,  before  using, 
the  longer  the  better,  and  finally  heated  to  the  full  temperature 
of  the  muffle,  so  that  they  are  red  all  through,  before  the  lead 
button  is  dropped  into  them.  If  they  are  moist  and  contain 
organic  matter,  they  will  "spit "  a.nd  throw  the  melted  lead  about, 


22  NOTES  ON  ASSAYING. 

thus  spoiling  the  assay.  Provided  the  button  will  go  into  the 
bowl  of  the  cupel  and  the  cupel  is  thick  enough,  it  will  absorb 
its  own  weight  of  PbO.  The  higher  the  temperature  the  more 
the  cupels  are  attacked  by  the  litharge. 

The  cracking  or  checking  of  cupels  may  be  due  to  different 
causes.  It  is  more  liable  to  occur  in  a  soft  cupel  than  in  a  hard 
one  and  in  one  which  is  heavily  charged  with  litharge  than  in 
one  where  only  a  small  amount  has  been  absorbed.  Too  sudden 
heating  and  the  presence  of  much  copper  may  cause  it. 

Cupels  can  be  used  only  once,  and  they  should  never  be 
heated  to  the  full  temperature  of  the  muffle,  taken  out,  again 
heated  and  used.  The  amount  of  lead  absorbed  as  oxide  is  from 
|  of  a  gramme  to  i  gramme  per  minute.  The  student  will  save 
time  and  also  danger  of  cracking  the  cupels  if  he  has  them 
warming  on  the  furnace  while  he  is  scorifying. 

Never  keep  lead  buttons  in  the  cupels  previous  to  using  them, 
for  it  injures  the  surface.  The  buttons  should  be  placed  in  the 
cupels  only  when  the  cupels  are  hot  and  ready  for  cupellation. 
Muffles. — These  hold  the  scorifiers  and  cupels.  They  are 
made  of  refractory  clay  and  come  in  various 
sizes  and  shapes,  some  with  high  and  some 
with  sloping  sides.  Most  of  them  are 
closed  at  one  end,  but  some  are  open  at 
both.  Some  have  projections  on  the  inside  the  whole  length  of 
the  muffle  and  about  half  way  up.  When  the  muffle  is  full  of 
cupels,  pieces  of  tile  or  false  muffle-bottoms  can  be  placed  across 
the  muffle  on  the  projections  and  above  the  cupels  which  are 
too  hot,  thus  lowering  the  temperature  and  keeping  it  uniform 
throughout.  The  size  is  indicated  by  letters: 

J  is  12"  long  X  6"  wide  X 4"  high,  outside  measurement. 
L"is"    "    Xg"     "   X6"    " 

The  L  will  weigh  about  13  Ibs. 

Original  casks  contain  50  ot  the  J's  and  25  of  the  L's. 
The  cost  depends  upon  the  size,  that  of  a  J  being  about  80  cts. 
The  length  of  time  they  last  depends  partly  on  the  way  in 


INTRODUCTION.  23-. 

which  they  are  supported  in  the  furnace  and  partly  on  the  care 
with  which  they  are  used. 

If  the  student  spills  anything  in  one  or  a  scorifier  eats  through,, 
he  should  immediately  scrape  out  the  substance  with  a  scraper, 
throw  in  some  ground  bone-ash  and 

scrape  it  out  again.     This  prevents  the     ^^  ^^\ 

slag  or  the   PbO   from  eating  a  hole 
through  the  muffle.     Finally  sprinkle  in  a  layer  of  bone-ash. 

The  life  of  the  muffle,  as  well  as  that  of  the  furnace,  is  pro- 
longed if  the  student  observes  the  following  precautions.  When 
he  is  through  using  a  furnace,  let  him  shut  off  all  drafts,  leave  the 
muffle  closed  and  the  furnace,  whether  muffle  or  crucible,  banked 
as  much  as  possible.  By  so  doing  all  parts  will  cool  down  slowly,, 
avoiding  danger  of  cracking. 


MORTARS   AND   LUTES. 

When  laying  bricks  or  making  repairs  about  a  furnace  where 
heat  is  used,  it  is  always  advisable  to  wet  the  bricks  and  the  places 
that  are  to  be  repaired,  previous  to  applying  the  mortar. 

Mortars  and  lutes  are  always  made  up  dry  and  thoroughly 
mixed  before  the  requisite  amount  of  water  is  added. 

Fire-bricks  are  laid  in  fire-clay  alone  or  a  mixture  of  f  ground 
fire-brick  and  J  fire-clay.  The  less  that  is  used  and  the  closer 
the  bricks  are  to  each  other  the  better. 

Muffles  may  be  set  in  place  with  a  mixture  of  3  parts  coarse 
fire-brick  (through  12  on  30  sieve),  i  part  fire-clay,  J  part  cement: 
or  §  ground  fire-brick  (through  i2-mesh  or  through  3o-mesh 
sieve)  and  J  fire-clay  with  a  few  pinches  of  Portland  cement. 
This  last  makes  the  mixture  adhere  better  and  also  makes  it 
firmer  and  harder.  Another  mixture  for  patching  furnaces,, 
where  the  brickwork  is  broken  or  torn  out,  consists  of 

7  parts  fire-brick  (through  12), 
2    '  *       cement, 
I  part  fire-clay. 


24  NOTES  ON  ASSAYING. 

If  this  is  put  on  as  dry  as  it  can  be  and  yet  stay,  so  as  not  T;o  shrink 
away,  it  will  make  a  patch  or  joint  as  solid  and  as  hard  as  the 
original  brick. 

Broken  muffles  may  be  made  to  last  many  days  longer  by 
judicious  patching  with  some  of  the  following: 

Where  the  bottom  is  almost  gone,  use  a  mixture  of 

2  parts  cement, 

i  part  ground  fire-brick, 

Ya  to  Y2  Part  fire-clay. 

For  patching  cracks  and  holes,  a  mixture  of  glass,  sand,  and 
clay,  to  which  a  few  pinches  of  litharge  have  been  added,  answers 
nicely  and,  after  one  good  heating,  becomes  as  hard  as  the  muffle. 

In  some  cases  I  have  used  with  good  results  a  paste  consisting 
of  asbestos  (short  fibre)  and  silicate  of  soda. 

Cement  used  at  Idaho  Springs,  Col,  for  muffles: 

Fire-clay,  2  parts, 
Litharge,    i  part, 
Bone-ash,  i     " 

For  patching  and  repairing  the  walls  of  crucible-furnaces 
use  the  first  mixture  recommended  for  setting  the  muffles.  Old 
graphite  crucibles  ground  and  used  alone  or  mixed  with  a  little 
fire-clay  make  a.  splendid  mixture  which  is  much  used  in  crucible- 
steel  works. 


CHAPTER  II. 
SAMPLING. 

Labelling  Samples. — Every  lot  or  sample  of  ore,  whether  in 
barrels,  sacks,  boxes,  or  bottles,  should  have  a  name  or  number 
attached  to  it.  When  the  sample  is  received,  the  first  thing  'to 
be  done  is  to  record  in  a  note-book  the  date  received,  name, 
number,  and  any  other  data  connected  with  it.  If  the  sample 
lias  no  number,  one  should  be  given  to  it  to  identify  it  in  the  future. 

Having  noted  the  number  of  sample,  region  produced,  date 
received,  etc.,  the  next  thing  to  do  is  to  obtain  the  gross  weight. 
If  the  ore  is  wet,  two  samples  of  from  5  to  20  kilogrammes  each 
are  taken  and  the  moisture  determined.  The  ore  is  now  dumped 
upon  the  sampling-floor  and  the  tare  of  the  boxes,  sacks,  or  barrels 
is  taken  and  the  net  weight  of  ore  obtained.  Next  the  student 
should  examine  the  ore  carefully  and  learn  all  he  possibly  can  in 
regard  to  the  gangue  and  the  minerals  contained  therein,  for  this 
can  be  done  better  while  the  ore  is  in  a  coarse  condition. 

The  sampling  comes  next,  and  is  done  by  gradual  crushing, 
mixing,  and  sampling  down  as  performed  according  to  the 
ring-and-cone  or  Cornish  method.  All  other  products  coming 
from  this  original  lot  should  also  retain  its  number.  For  in- 
stance : 

Sample  No.  1420.         Lead  Ore  from  Missouri. 
"    1420-1.      Heads  from  jig  A. 
"    1420-2.      Tailings  from  jig  A. 

Any  part  of  the  sample  not  to  be  used  in  the  test  or  assay 
should  be  immediately  put  in  sacks,  boxes,  or  barrels.  All 
products,  of  every  description,  whether  in  sacks,  hods,  pails,  or 
boxes,  should  be  labelled  in  some  way,  otherwise  they  are  liable  to 
be  misplaced  or  thrown  away.  If  to  remain  about  the  labora- 

25 


26  NOTES  ON  ASSAYING. 

tory  for  any  length  of  time,  they  should  be  covered  up  and  not 
left  in  open  receptacles. 

By  observing  these  few  precautions  no  products  can  be  lost, 
misplaced,  or  contaminated,  as  is  so  often  the  case.  The  student 
should  bear  constantly  in  mind  that  if  one  product  is  lost,  the 
final  summing  up  of  the  test  or  run  is  made  impossible. 

In  taking  up  this  work  I  shall  give  general  directions  as  to  the 
methods  employed,  but  shall  say  nothing  in  regard  to  how  far 
a  lot  of  ore,  of  a  certain  size  or  richness,  can  safely  be  cut  down. 
Owing  to  certain  experiments  still  going  on,  I  am  led  to  believe 
that  no  rule  can  be  laid  down  in  regard  to  this,  and  that  each 
lot  of  ore  is  a  case  by  itself. 

I  do  believe,  however,  that  every  final  sample  should  be 
crushed  through  a  120-  or  i/p-mesh  sieve  at  least.  The  finer 
the  sample,  the  greater  the  probability  of  obtaining  uniform 
results.  If  there  were  only  some  machine  which  would  do  it 
easily  and  rapidly,  and  not  contaminate  the  sample,  I  would 
crush  every  final  sample  through  a  2oo-mesh  sieve.  Many  errors 
in  assaying  and  chemical  work,  as  well  as  non-uniformity  in 
results  by  different  analysts  on  the  same  sample,  are  due  simply 
to  the  sample  being  in  a  too  coarse  condition.  To  send  samples 
(other  than  metallic  drillings)  which  might  be  passed  through 
a  2oo-mesh  screen,  but  have  not  been  so  treated,  to  different 
assayers  and  chemists  in  order  to  make  a  comparison  of  dif- 
ferent methods  seems  to  me  not  only  a  waste  of  time,  but  I 
believe  that  entirely  erroneous  conclusions  may  be  drawn  from 
the  data  collected. 

Furthermore,  when  any  experimental  work  is  undertaken  on 
a  given  sample  be  sure  that  this  sample  is  so  large  that,  as  it 
diminishes  in  size,  all  possibility  of  its  changing  is  eliminated. 

In  all  sampling  work,  the  student  should  bear  constantly  in 
mind  two  important  things: 

i  st.  That  each  step  in  the  process  must  be  thoroughly  and 
carefully  performed. 

2d.  That  every  piece  of  apparatus  or  machine  must  be  clean 
and  free  from  all  dust  and  ore  previous  to  its  being  used. 

By  adhering  to  these  rules  one  ought  to  obtain  a  correct 
sample  for  assay  or  analysis;  by  disregarding  them  one  will 


SAMPLING.  27 

not  only  obtain  an  Incorrect  sample,  but  will  find  minerals  in  the 
sample  that  were  never  present  in  the  original  ore. 

Ores  may  be  sampled  in  three  ways,  each  of  which  has  its 
advocates : 

1.  By  coning  and  quartering,  the  Cornish  method. 

2.  Automatically  by  machines,  especially  applicable  to  sam- 
pling-mills, where  the  whole  stream  of  ore,  after  leaving  crusher  or 
rolls,  is  taken  at  given  intervals. 

3.  Automatically  by  machines,  also  applicable  to  sampling- 
mills,  where  a  part  of  the  stream  of  ore  is  taken  all  the  time. 

The  first  method  will  be  described  in  these  notes. 
We  may  divide  our  material  into  two  classes: 

A.  Large  lots  containing  over  4000   Ibs.,  also  waste-dumps, 
gravel,  placer,  and  similar  deposits. 

B.  Lots  of  4000  Ibs.  and  under. 

Class  A. — If  the  material  of  this  class  is  in  heaps  and  in  a 
fine  condition,  it  may  be  very  accurately  sampled  in  the  following 
ways: 

i  st.  By  digging  cuts  or  holes  into  the  piles  in  every  direction 
and  taking  out  50  to  100  Ibs.  from  each  place. 

2d.  By  boring  holes  into  it  in  various  places  with  a  large  auger 
2"  to  6"  in  diameter,  fitted  to  a  long  iron  handle. 

The  borings  should  fall  upon  a  piece  of  canvas,  and  all  borings 
should  be  saved. 

In  both  methods  all  the  portions  from  the  various  holes  are 
put  together,  thoroughly  mixed,  sampled,  and  quartered  down  in 
the  manner  described  under  Class  B. 

If  the  ore  is  in  coarse  large  lumps,  it  is  best  sampled  by  means 
of  the  tape-line.  This  method  is  much  used  on  iron  ores.  A  100- 
or  2oo-foot  measure  is  taken  and  dropped  over  and  around  the 
ore-pile  in  different  directions.  Take  a  part  or  the  whole  of  every 
piece  of  ore  upon  which  each 
foot-mark  of  the  tape  rests. 
Any  laborer  can  do  this,  as 
there  is  no  question  of  judg- 
ment about  it.  Where  a  sample  is  taken  by  selecting  pieces 
here  and  there  all  over  a  pile  it  is  extremely  difficult  to  obtain 
a  fair  average,  for  a  person's  judgment  is  influenced,  in  spite  of 


28  NOTES  ON  4SS4YING. 

himself,  by  the  appe:  ranee  of  the  individual  pieces,  and  this  is 
particularly  true  where  he  is  thoroughly  acquainted  with  the 
character  of  the  ore  being  sampled.  The  sample,  when  obtained, 
is  crushed  and  treated  as  described  under  B. 

If  the  ore  comes  in  cars,  which  generally  hold  from  15  to  30 
tons,  it  is  either  in  a  loose  condition  or  in  sacks.  (If  rich,  it  is 
always  in  sacks.)  If  it  is  in  sacks,  it  is  first  weighed,  and  if  of  low 
grade,  i.e.,  below  100  oz.  silver  per  ton,  every  fifth  or  tenth  sack  is 
taken  out  and  conveyed  to  the  sampling- floor.  If  it  is  of  high 
grade,  every  fifth  sack  is  taken.  This  brings  the  sample  down  to 
3000  to  6000  Ibs.  If  the  ore  is  loose  in  the  car,  a  space  is  cleared 
in  the  centre  and  every  fifth  or  tenth  shovelful  is  set  aside  for  the 
.sample.  If  ore  is  rich,  every  third  is  set  aside,  the  remainder 
going  to  the  ore- bins.  This  process  is  repeated  until  the  sample 
representing  each  car  weighs  from  3000  to  4000  Ibs.  If  the  ore 
is  moist,  two  samples,  each  weighing  at  least  5  kilogrammes, 
should  be  taken  at  this  time  to  determine  the  moisture. 

Having  our  sample  of  ore,  weighing  in  this  case  3000  to  4000 
Ibs.  and  representing  the  total  amount  of  ore  received  in  the  car, 
the  whole  is  treated  as  in  Class  B. 

If,  in  any  of  the  previous  samples  the  pieces  of  ore  are  over 
-f "  in  size,  the  whole  sample  is  crushed. 

Before  crushing  a  new  lot  of  ore  be  sure  that  the  machines 
are  perfectly  clean  and  free  from  the  previous  lot  treated;  for  unless 
Ms  is  done,  if  that  lot  of  ore  was  rich,  the  present  sample  will 
be  worthless. 

Class  B. — Having  all  the  ore  crushed  through  a  J"-mesh 
screen,  spread  it  in  a  circle  and  treat  it  according  to  the  Cornish 
method,  which  is  here  given. 

The  ore  is  first  shoveled  into  a  conical  heap  in  the  centre  of 
the  circle  of  ore,  the  centre  of  each  shovelful  striking  the  apex 

of  the  cone  and  running  down 
evenly  all  round.  Spread  out 
flat  and  again  draw  into  a  circle, 
or  else  start  a  fresh  pile  and 
keep  repeating  until  it  is  certain 
that  the  lot  of  ore  is  thoroughly  mixed.  This  conical  heap,  8'  or 
more  in  diameter  and  about  3^'  high,  is  next  drawn  out  into 


SAMPLING. 


the  form   of  a  truncated  cone  from  6"  to  12"  deep  and  divided 
into  quarters. 

Quarters  a'  and  a"  are  saved;  quarters  xf  and  oc"  go  to  the  ore- 
bins.  The  quarters  saved  are  mixed  as  before  and  shoveled  into  a, 
cone;  a  shovelful  is  first  taken  from  a'  and  then  one  from  a"  and 
quartered  again.  This  time  quarters  x/  and  x/'  are  saved.  Now 
cone  and  quarter  again,  mixing  by  first  taking  a  shovelful  from  yf 
and  then  from  x".  If  the  sample  was  originally  4000  Ibs.,  it  is 
now  500  Ibs.  This  is  crushed  in  rolls  to  J"  size  and  after  being^ 
thoroughly  mixed  as  before  it  is  coned  and  quartered  down  to 
250  Ibs.  It  is  crushed  again  in  rolls,  the  whole  250  Ibs.  passing; 
through  an  8-mesh  sieve  (i.e.,  a  sieve  with  8  meshes  to  the  linear 
inch.  Wire  occupies,  say,  .0280"  X  8,  or  .224";  therefore  meshes, 
must  be  .097"  each  instead  of  .125").  It  is  mixed  thoroughly  again 
and  sampled  down  to  125  Ibs.  This  is  crushed  in  some  machine 
so  that  it  will  pass  through  a  12 -mesh  sieve.  The  mixing  and 
quartering  down  must  now  be  repeated  until  the  sample  weighs 
about  30  Ibs.  In  all  this  quartering  down  one  must  be  very 
careful  to  have  the  fine  portion  of  the  ore  belonging  to  each 
quarter  go  with  it,  and  not  all  left  each  time  upon  the  floor  to  go> 
with  other  quarters.  Always  weigh  the  ore  before  passing  it 
through  any  sieve. 

The  30  or  more  pounds  of  ore  are  put  through  a  30-  or  4o-mesh 
sieve  and  quartered  and  sampled  down 
to  2  to  4  Ibs.  This  is  best  done,  be- 
cause it  avoids  making  dust,  by  using 
a  split  shovel  which  is  placed  in  a 
pan  and  the  ore  passed  over  it  by 
means  of  a  wide  shovel,  from  aa  to  bb. 

(/  i/~ 

When    the    gutters   are  full  the  split 

shovel  is  emptied  and  this  ore  kept  separate.     This  is  repeated 

until  the  sample  is  all  passed  over  the  split  shovel. 

If  what  goes  between  the  gutters  is  saved  the  first  time, 
what  fills  the  gutters  is  saved  the  next  time,  and  so  on  until  the 
30  Ibs.  is  reduced  to  the  desired  quantity.  Or  the  whole  30  Ibs. 
is  crushed  through  a  40- mesh  sieve,  a  sample  of  150  to  200 
grammes  taken  from  this,  with  a  broad  spatula  with  high  sides, 


and 
„  i     12  guttera 
T1    l"high 
|    X'wide 

.1- 

3°  NOTES  ON  ASSAYING. 

and  crushed  through  a  loo-mesh  or  finer  sieve.     If  the  sample 
is  at  all  damp,  it  is  next  dried  at  100°  C. 

^2~~  I         J    for  f  of  an  hour,  weighed,  and  the  whole 

amount  crushed   upon  a  grinding-plate  or 

bucking- board  and  passed  through  a  100-,  120-,  or  140- mesh  sieve. 

Small  hand  samples  and  specimens,  weighing  600  grammes 
or  under,  should  be  crushed  and  all  passed  through  the  fine  sieve. 

The  bucking-board  must  be  perfectly  clean  before  it  is  used. 
If  any  residue  or  particles  of  gold  or  silver  are  left  on  this  sieve, 
they  are  weighed,  wrapped  in  C.P.  lead-foil,  and  cupelled.  The 
resulting  button  is  weighed  and  parted  for  gold. 

If  the  particles  are  suspected  of  being  gold  alone,  the  residue  is 
wrapped  in  C.P.  lead,  a  piece  of  C.P.  silver  added,  and  the 
whole  cupelled  and  then  parted  for  gold. 

These  weights  and  the  weight  of  the  ore  before  passing  it 
through  the  sieve  being  known,  the  number  of  ounces  per  ton 
can  be  calculated  and  reported  as  so  much  free  gold  or  silver,  and 
they  can  be  added  to  the  assay  of  the  ore  passing  through  the 
loo-,  1 20-,  or  i4o-mesh  sieve.  (See  Calculation  of  Pellets.)  This 
question  of  metallic  particles  applies  as  well  to  the  other  sieves 
used,  and  the  finer  the  sieve  the  greater  the  care  to  be  observed 
in  regard  to  these  particles.  The  method  of  attempting  to  force 
-free  gold  or  other  metallic  particles  through  a  sieve,  by  con- 
tinually grinding  them  with  some  of  the  ore  already  pulverized, 
is  extremely  bad  practice.  It  consumes  a  large  amount  of  time 
and  if  the  particles  are  coarse  they  cannot  be  forced  through 
a  fine  sieve.  Furthermore  it  coats  the  machines  and  bucking 
board  with  a  film  of  the  metal  which  it  is  difficult  to  remove 
and  it  makes  the  fine  ore,  which  otherwise  might  be  quite  even 
.and  uniform,  very  uneven. 

The  fine  portion  of  the  sample,  i.e.,  the  part  which  has  passed 
through  the  ico-mesh  or  finer  sieve,  is  put 
upon  a  sheet  of  glazed  paper,  rubber,  or  oil- 
cloth and  thoroughly  rolled  over  and  over 
again  for  100  times  at  least.  It  is  then 
spread  out  thinly  and  divided  into  squares 
_as  in  the  annexed  figure.  A  portion  is  taken 


SAMPLING.  '31 

with  a  spatula  from  each  and  every  square,  representing  a  sec- 
tion from  the  top  of  the  ore  to  the  oilcloth  (that  isy  do  not  take 
the  upper  surface  of  the  ore  alone). 

Fill  from  one  to  five  eight-ounce  bottles.  The  contents  of 
these  bottles  should  be  identical  and  should  represent  a  fair 
average  of  the  original  ore,  whether  it  was  a  carload  lot  or  a  sack 
of  ore. 

In  all  the  previous  work  every  precaution  should  be  taken 
against  making  dust  and  losing  the  fine  ore. 

The  ore  is  now  ready  to  be  assayed,  for  passing  an  ore  through 
a  loo-,  1 20-,  or  i4o-mesh  sieve  generally  makes  it  sufficiently  fine 
for  assay  purposes.  In  some  special  cases  it  must  be  pulverized 
even  more  finely.  In  weighing  out  the  ore,  always  empty  the  entire 
ore  out  of  the  bottle  or  its  receptacle  and  thoroughly  mix  it  by  rolling 
it  over  and  over  at  least  100  times. 

This  is  particularly  necessary  if  the  bottle  has  stood  any  length 
of  time,  for  some  ores  seem  to  stratify  quite  readily  on  standing. 
The  coarser  the  ore  and  the  greater  the  difference  in  the  specific 
gravity  between  the  heaviest  and  the  lightest  particles  the  more 
likely  is  this  to  occur. 

Weigh  out  the  ore  just  as  carefully  as  you  can  upon  the  pulp- 
balances  and  assay  in  the  usual  manner  for  whatever  element  you 
are  determining. 

Report  the  results  for  silver  and  gold  in  ounces  troy  per 
2000  Ibs.  of  ore  av.  Metals  such  as  lead,  copper,  tin,  etc.,  are 
reported  in  percentages.  If  the  ore  carries  free,  i.e.,  native,  gold 
or  silver,  it  may  also  be  reported  as  follows: 

Gold  (free),  i.e.,  on  sieve oz.  per  ton 

•Gold  in  fine  ore,  through  sieve "     "     " 


Total "      "     " 

At  $20.67  Per  oz-  (U-  S.  standard  value)  =$ 

Silver  is  reported  in  the  same  way  as  gold,  but  the  vaiue  is 
figured  at  the  market  rate,  which  of  course  varies  from  time  to 
time. 

It  has  been   said  that   all  machines   should  be  thoroughly 


3*  NOTES  ON  ASSAYING. 

clean  before  any  sample  of  ore  is  passed  through  them,  and  the 
following  example  will  show  why  this  is  so  essential : 

About  6  Ibs.  of  ore  carrying  free  gold  and  running  550  oz. 
to  the  ton  was  crushed  in  one  of  the  ordinary  rotary  sample-mills. 
123.6  grammes  of  fine  quartz  sand  was  then  run  through  the 
machine.  This  sand,  previous  to  passing  through,  assayed  .04  oz. 
in  gold;  after  passing  through  it  ran  .78  oz.  Two  more  lots  of 
quartz  carrying  .03  oz.  of  gold,  and  weighing  480  and  555 
grammes  respectively,  were  passed  through  the  machine,  and  the 
last  lot  assayed  .15  oz.  of  gold. 

What  applies  to  a  machine  also  applies  to  the  bucking-board,, 
which  should  always  be  thoroughly  cleaned  by  crushing  at  least 
two  lots  of  clean  sand  upon  it;  and  if  an  unusually  rich  sample 
has  been  pulverized  upon  it,  even  a  more  thorough  cleaning 
should  be  given  to  it. 

Too  much  care  cannot  be  given  to  this  part  of  the  assay  work,, 
for  I  have  known  many  inaccurate  assays  to  result  from  lack  of 
it,  and  several  instances  where  worthless  ore  was  reported  as 
carrying  values. 

ORES    CARRYING    METALLIC    PARTICLES. 

Gold  and  silver  ores  carrying  metallic  particles,  and  others,, 
such  as  the  copper  ore  of  Lake  Superior,  will  leave,  when  crushed 
and  passed  through  a  sieve,  more  or  less  of  the  metal  upon  it, 
the  amount  depending  on  the  coarseness  of  the  particles  and  the 
size  of  the  mesh  of  the  sieve. 

The  coarser  the  particles  are  and  the  more  numerous,  the 
more  difficult  it  is  to  obtain  a  sample  which  represents  the  originrl 
ore,  therefore  our  aim  should  be  to  remove  these  particles  rt 
every  opportunity.  By  so  doing,  although  we  may  not  prevent 
all  the  metallic  particles  passing  through  the  sieve  into  our  final 
sample,  the  fineness  of  these  particles  makes  it  more  likely  that 
we  will  obtain  uniform  assays  than  if  the  particles  were  coarser 
and  more  numerous. 

When  these  pellets  are  met  with,  students  always  seem  to  have 


SAMPLING.  33. 

difficulty  in  calculating  their  results.  If  they  bear  the  following 
in  mind,  this  difficulty  ought,  in  great  part,  to  disappear. 

Weigh  the  original  sample. 

Weigh  the  ore  before  passing  it  through  a  sieve. 

Weigh  and  determine  the  amount  of  metal  on  each  sieve,, 
and  know  from  how  much  ore  it  has  come. 

Weigh,  assay,  or  analyze  the  fine  ore  passing  through  the  last, 
sieve. 

Calculate  the  total  amount  of  metal  in  the  entire  sample 
of  ore. 

From  this  result  and  the  weight  of  the  original  sample  calcu- 
late the  per  cent  of  metal  or  the  ounces  per  ton. 

The  following  will  serve  as  examples,  and  it  should  be  noticed 
that  the  amount  of  the  material  left  upon  the  sieve  or  sieves,, 
the  richness  of  this  material,  and  the  percentage  which  it  is  of 
the  whole  sample  has  everything  to  do  with  the  final  results. 
They  may  be  higher  or  lower  than  the  analysis  of  the  finest  ore 
passing  through  the  final  sieve. 

EXAMPLE  I.  A  sample  of  lead  dross  weighs  100  grammes  and 
is  crushed  through  a  20-mesh  sieve. 

Lead  pellets  on  sieve  weigh  40  grammes. 

Material  through  the  sieve  weighs  59  grammes  (assays  10%  Pb)* 

Loss  in  grinding,  i  gramme. 

The  total  lead  =  40  grammes  on  the  sieve. 

Lead  in  fine  material,  supposing  the  gramme  lost  to  assay 
the  same  as  the  59  grammes  passing  through  the  sieve  =  6  grammes. 
Total  =  46  grammes. 

-  =46%  of  lead  in  the  dross. 

EXAMPLE  II.  A  sample  of  ore,  carrying  metallic  copper,, 
weighs  94  grammes  and  is  crushed  through  a  1 20- mesh  sieve. 

Residue  on  the  sieve  weighs  10  grammes  and  yields  on  analysis 
9.32  grammes  of  copper.  The  fine  ore  (84  grammes)  through 
the  sieve  analyzes  20.38%  copper. 


34  NOTES  ON  ASSAYING. 

84X20.38%  contain  17.12  grammes  copper 
Pellets  contain    .9.32          "  " 


Total  =  26. 44 

26 .44 

—  =28.13%  copper  in  the  ore. 
94 

EXAMPLE  III.  Sample  of  concentrates,  carrying  free  gold, 
weighs  35  grammes  and  is  crushed  through  a  i2o-mesh  sieve. 
The  residue  on  the  sieve  weighs  2  grammes  and  consists  of  pieces 
of  iron  and  free  gold.  On  cupellation  and  parting,  it  yields 
.00015  grammes  of  gold. 

The  fine  concentrates  through  the  i2O-mesh  sieve  (33  grammes) 
assay  4.09  oz.  per  ton. 

A    T1        Ore  through          Gold  in 
1  A>  *•         1 20  Sieve.  i  A.  T. 

29.16     :     33     ::     .00409     :     #  =  .00463 
Gold  found  in  residue  on  the  sieve  =  .00015 


Total  gold  in  sample  =  .00478 
•*•   35  :  29.16  •  •  .00478  :  #=.00398. 

Concentrates  assay  3.98  oz.  gold  per  ton  of  2000  Ibs.  This  makes 
the  final  result  lower  than  that  of  the  fine  concentrates  passing 
through  the  sieve,  and  is  due  to  the  large  amount  of  material  left 
on  the  sieve  and  its  being  poorer  in  gold  than  the  remainder  of 
the  concentrates.  It  also  shows  that  it  would  be  incorrect  to 
find  the  ounces  of  gold  in  the  two  grammes  of  residue  and  add 
this  result  to  the  ounces  (4.09  oz.)  found  in  the  fine  concentrates. 

EXAMPLE  IV.  A  sample  of  ore,  carrying  free  gold,  weighs  57 
grammes  and  is  crushed  through  a  120- mesh  sieve.  The  residue 
on  the  sieve  consists  of  pieces  of  mica  and  free  gold  and  weighs  10 
grammes.  On  scorifying,  cupelling,  and  parting  it  yields  .0630 
grammes  of  gold.  The  fine  ore  through  the  sieve  assays  2.62  oz. 
per  ton. 

29.16  :  47  : :  .00262  :  #  =  .00422 
Gold  on  sieve  =  .0630 


Total  gold  in  ore  =  .06722  grammes. 
57  :  29.16  : :  .06722  :  #  =  .03438. 


SAMPLING.  35 

Ore  assays  34.38  oz.  gold  per  ton  of  2000  Ibs.  In  this 
case  the  material  left  upon  the  sieve  is  very  much  richer  than 
the  fine  material  passing  through  the  sieve,  hence  the  final  result 
is  higher  than  the  assay  of  the  fine  material.  In  this  example  it 
can  be  readily  seen  how  absurd  it  would  be  to  find  the  ounces 
which  the  residue  on  the  sieve  assays  and  then  add  the  result  to  the 
assay  of  the  fine  ore  passing  through  the  sieve. 

The  examples  given  are  not  made  up,  but  are  some  which 
have  been  met  with  in  actual  work.  In  all  of  them  the  material 
which  is  lost  in  grinding  and  sampling  is  assumed  to  assay  the 
same  as  the  fine  material  passing  through  the  last  sieve.  We 
really  know  nothing  about  this  lost  ore,  whether  it  is  richer  or 
poorer  than  the  ore  that  is  assayed.  It  may  be  richer,  it  may  be 
poorer,  but  it  has  got  to  be  taken  account  of,  and  I  think  it  fair 
to  consider  the  ore  lost  to  assay  the  same  as  the  fine  ore. 

Where  pellets  are  left  on  a  sieve  with  other  matter  it  is  always 
better  to  treat  the  whole  material.  For  instance,  if  free  gold  and 
metallic  iron  are  in  the  residue,  it  is  not  always  safe  to  remove  the 
iron  with  a  magnet,  for  some  of  the  gold  may  have  been  pressed 
hard  on  to  the  iron,  and  when  the  iron  is  removed  the  gold  goes 
with  it. 


CONCENTRATION  BY  PANNING  OR  VANNING. 

This  is  to  determine  the  percentage  of  concentrates  in  an  ore 
or  to  separate  any  material  of  value  from  that  which  has  no 
value,  i.e.,  waste  or  tailings. 

Take  the  ore  you  sampled  (through  30-  or  4o-mesh  sieve),  or 
else  take  20  grammes  of  pyrite  (sp.  gF.  4.95  to  5.10)  and  150 
grammes  of  quartz  (sp.  gr.  2.65),  and  recover  the  concentrates 
from  the  ore  or  the  pyrite  from  the  quartz. 

First,  record  in  your  note-book  all  the  data  upon  the  bottles,  bags, 
or  samples  given  you. 

Second,  order  from  the  supply-room  two  gold-pans  and  one 
six-inch  evaporating-dish. 

If  the  ore  you  sampled  is  rich  in  sulphides,  weigh  out  100 


OAT  ASSAYING. 


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SAMPLING. 


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' 


38  NOTES  ON  ASSAYING. 

grammes  of  it  on  the  flux-balance;  if  poor,  200  grammes.  If  you 
are  working  upon  the  pyrite  and  quartz,  weigh  the  pyrite  on  the 
pulp-balance  and  the  quartz  on  the  flux-balance.  Put  the  ore 
into  one  gold-pan  (or  the  pyrite  with  the  quartz  over  it),  moistea 
very  thoroughly  to  make  any  float  material  sink,  fill  the  pan  nearly 
full  of  water,  allow  to  stand  ten  or  fifteen  minutes,  and  then 
pan  the  material  from  this  pan  into  the  other.  The  panning 
is  done  by  having  the  ore  covered  with  water  and  the  contents 
of  the  pan  thoroughly  liquid.  While  shaking  well,  to  allow  the 
heavy  material  and  concentrates  to  settle  out,  give  the  pan  a 
rotary  or  side  motion  and  every  now  and  then  throw  some  of  the 
gangue  or  lighter  material  over  the  edge.  Continue  to  d3  this  until 
no  more  gangue  can  be  removed  without  washing  over  some  of 
the  concentrates.  Transfer  concentrates  to  the  evaporating-dish 
and  save.  Pan  the  ore  over  again,  and  repeat  until  you  can  obtain 
no  more  concentrates  or  pyrite.  Do  not  throw  away  any  water 
or  waste  ore.  Allow  the  concentrates  in  the  6"  evaporator  to 
settle  for  some  time  and  then  carefully  decant  the  H^O.  Dry 
carefully  and  as  quickly  as  possible,  but  do  not  make  so  hot 
that  the  concentrates  will  begin  to  roast,  and  weigh  on  the  pulp- 
balance.  Allow  tailings  or  waste  to  stand  some  time,  decant 
off  H2O,  transfer  to  an  agate  pan  or  bowl,  dry,  and  weigh  on 
flux-balance.  The  iron  gold-pans  must  not  be  heated  or  the 
material  left  in  them,  for  they  rust  and  are  ruined.  Clean  themy 
dry  them,  and  return  to  the  supply-room  at  the  end  of  the  exercise. 

Make  your  report  as  follows: 

No.  of  ore  1360.     Amount  taken=ioo  grammes. 

Concentrates  (FeS2,  PbS,  and  ZnS) 10  grammes,  10% 

Tailings 86        "  86% 

Slimes  or  ore  lost  in  process 4  4% 

100       "          100% 


CHAPTER  III. 
ASSAY  OF  ORES  FOR  SILVER. 

THE  assay  of  ores  for  silver  is  taken  up  separately  from  the 
assay  for  gold,  because  my  experience  has  been  that  a  beginner 
can,  in  this  way,  learn  the  methods  of  both  assays  much  more 
easily.  By  taking  up  the  silver  first,  he  has  one  thing  in  mind, 
not  two ;  he  becomes  familiar  with  the  s  pparatus  employed,  the 
chief  methods  used,  the  making  up  of  different  charges,  and  the 
metal  to  be  determined  is  present  in  fairly  large  amount. 

After  this  he  is  much  better  able  to  take  up  the  assay  of  ores 
wherein  the  metal  to  be  determined  is  present  in  much  smaller 
amount  and  which  necessarily  requires  more  care  in  treatment. 

Silver  fuses  at  961.5°  C.  or,  according  to  Berthelot,  at  962°  C. 
(1898).  Atomic  weight  =  107. 9.  Sp.gr.  =  10.5. 

Ores  containing  silver  may  be  assayed  by  fire  in  either  of  two 
ways: 

First.  By  the  scorification  method. . 

Second.  By  the  crucible  method. 

In  either  case  the  object  is: 

i  st.  To  add  some  flux  or  fluxes  to  the  ore  to  combine  with 
the  gangue  and  impurities,  leaving  a  slag  free  from  precious 
metals. 

2d.  To  mix  some  granulated  lead  or  litharge  with  the  ore,  by 
means  of  which  the  silver,  together  with  the  gold,  is  collected  and 
alloyed  with  the  lead. 

3d.  To  separate  the  lead  from  the  silver  and  gold  by  means  of 
cupellation. 

The  silver  in  the  ores  may  be  native  or  may  occur  as  real 
silver  ores,  i.e.,  ores  with  a  definite  composition,  as  cerargyrite 

39 


-40  NOTES  ON  ASSAYING. 

(AgCl)  75.26%  silver,  argentite  (Ag2S)  87.1%  silver,  etc.,  but 
in  the  majority  of  ores  it  is  derived  from  argentiferous  minerals, 
such  as  galenite,  blende,  pyrite,  cerussite,  etc.,  occurring  in  some 
gangue  as  quartz,  limestone,  porphyry,  slate,  granite,  etc. 

SCORIFICATION    METHOD. 


(The  Greek  word  GKopia  means  slag,  i.e.,  this  is  a  slag- 
making  process.)  This  is  the  more  simple  of  the  two  methods, 
and  although  adapted  to  most  ores  is  especially  so  to  copper 
mattes,  copper  ores,  ores  rich  in  antimony,  zinc  residues,  and 
similar  substances.  It  is  an  oxidizing  process  and  these  impurities 
(Cu,  Sb,  and  Zn)  are  oxidized  directly  by  the  air,  or  by  the  litharge 
formed  in  the  process,  and  volatilize  as  oxides,  or  else  pass  into 
the  slag  or  waste  material. 

In  the  crucible  process  Cu,  Sb,  and  Zn,  which  we  wish  to 
eliminate,  are  liable  to  be  reduced  and  to  pass  into  the  lead  button, 
and  have  to  be  subsequently  removed. 

Ordinary  Ores.  —  The  process  is  carried  out  as  follows:  Take 
the  sample  (if  it  is  in  a  bottle  or  receptacle,  empty  the  'whole  of  it 
out)  and  roll  it  on  oilcloth  or  glazed  paper  at  least  100  times. 
This  is  especially  necessary  where  a  sample  has  just  been  ground 
or  has  stood;  by  standing,  samples  are  apt  to  layer  or  stratify, 
and  the  longer  an  ore  has  stood  and  the  greater  the  difference 
in  the  specific  gravity  of  the  constituents  of  the  sample,  the  more 
thorough  this  mixing  should  be.  If  two  substances  of  different 
specific  gravity  and  color,  like  soda  and  litharge,  are  put  on  a 
paper,  it  will  be  found  that  a  very  thorough  mixing  is  necessary 
before  the  whole  mass  becomes  perfectly  homogeneous. 

Weigh  out  very  carefully  two  portions  of  ore,  of  -^  A.  T. 
each,  on  the  pulp-balances.  The  ore  should  be  fine  enough  to 
pass  through  a  loo-mesh  sieve  at  least,  i.e.,  100  meshes  to  the 
linear  inch.  Place  the  weighed  amounts  of  ore  in  two  scorifiers 
(2^"  and  2f"  in  diameter  respectively),  carefully  brushing  out 
the  scale-pan  each  time.  On  the  flux-balances  weigh  carefully 
35  grammes  of  granulated  lead  and  mix  approximately  one  half 


ASSAY  OF  ORES  FOR  SILVER.  4* 

of  this  with  the  ore  in  the  2\"  scorifier,  and  place  the  other  half  on 
top.  Then  weigh  45  grammes  of  lead  and  treat  the  other  por- 
tion of  the  ore  with  it  in  the  same  way.  Place  a  pinch  of  borax 
glass  (about  i  gramme)  on  the  top  of  the  contents  of  each  scori- 
fier. The  scorifiers  are  now  ready  for  the  muffle,  which  has  been 


D 


Scorifier-tongs. 

previously  heated  and  which  should  now  be  very  hot.  By  means 
of  the  scorifier-tongs  place  them  in  the  muffle  and  close  the  door. 

Fusion  Period. — The  door  of  the  muffle  should  be  kept  closed 
some  time,  to  allow  the  contents  of  scorifiers  to  become  thoroughly 
fused.  Oftentimes  the  scorifieis  spit  owing  to  the  air  being 
admitted  too  soon,  which  occasions  too  violent  oxidation. 

Roasting  Period. — Open  the  door  of  the  muffle  and  admit  a 
full  supply  of  air.  The  ore  and  lead  have  now  either  become  per- 
fectly liquid  or  else  small  patches  of  ore  are  seen  on  the  lead  bath. 

In  either  case  a  full  supply  of  air  is  necessary  to  roast  and 
oxidize  the  impurities  in  the  ore  and  also  to  oxidize  the  lead  to 
litharge  (PbO).  This  and  the  air  are  our  decomposing  agents; 
by  means  of  them  volatile  substances  like  As  and  Sb  are  oxi- 
dized to  As2O3  and  Sb2O3,  and  either  volatilize  as  such  or  else  pass 
into  the  slag. 

Scorification  Period. — Metals  like  copper  and  zinc  partly  slag 
off  and  partly  go  into  the  lead  button.  Any  sulphur  in  com- 
bination with  these  and  other  metals  is  oxidized  to  SO2  and 
volatilizes. 

The  vapor  arising  from  the  assays  will  often  indicate  the 
character  of  the  ore.  Sulphur  gives  clear  gray  vapor;  arsenic, 
grayish  white;  and  antimony,  reddish.  Zinc  vapor  is  blackish 
and  the  zinc  burns  with  a  bright  white  flame. 

//  the  contents  of  the  scorifiers  do  not  become  thoroughly  liquid 
and  do  not  show  a  good  clear  lead  surface,  the  assays  need  either 
more  heat,  more  borax  glass,  or  more  lead. 

If  the  assay  is  in  a  satisfactory  condition  during  the  roasting 


42  NOTES  ON  ASSAYING. 

and  scorification  periods  the  litharge  formed  partly  combines 
with  the  gangue  of  the  ore  and  partly  with  the  material  of  the 
scorifier  itself.  The  slag  thus  formed  goes  to  the  circumference 
of  the  scorifier,  leaving  a  lead  surface  or  eye  exposed.  (If  the 
muffle  is  too  cold,  the  litharge  formed  will  make  a  film  over  the 
eye  of  lead  and  the  scorification  stops.) 

The  slag  gradually  increases,  the  lead  eye  grows  smaller  and 
smaller,  and  finally  the  slag  closes  over  and  completely  covers  the 
lead. 

The  scorification  period  is  now  ended.  The  ore  ought  to  be 
completely  decomposed  and  the  slag  quite  free  from  or  very  low- 
in  silver,  and  the  remainder  of  the  silver  and  gold  in  the  ore  should 
be  alloyed  with  the  lead. 

Liquefaction  Period. — Close  the  door  of  the  muffle  and  increase 
the  heat  for  a  few  minutes  to  make  the  contents  of  the  scorifiers 
thoroughly  liquid  and  to  insure  a  clean  pour. 
Pour  the  contents  into  a  mould  which  has  been 
coated  with  chalk,  iron  oxide,  or  oil,  previously 
warmed  and  dried.  The  inside  surface  of  the 
scorifiers  should  be  clean  and  show  no  lumps 
of  ore  or  undecomposed  material. 

When  cold,  break  the  lead  from  the  slag,  which  should  be 
perfectly  free  from  any  small  lead  buttons;  these  are  most  likely 
to  be  on  the  circumference  of  the  slag.  Hammer  the  lead  into 
the  form  of  a  cube  and  weigh  on  the  flux-balance.  If  this  lead  is 
soft  and  malleable,  it  is  ready  for  cupellation.  (See  Cupellation> 
page  55.)  If  it  is  hard  or  brittle,  it  may  contain  impurities  which 
must  be  removed  by  rescorifying  with  an  additional  amount  of 
granulated  lead.  (See  Rescorifying  Buttons.) 

Brittle  buttons  may  be  due  to  Cu,  As,  Sb,  Zn,  S,  PbO,  or  a  rich 
alloy  oj  Pb  and  Ag  or  Pb  and  Au.  Hard  buttons  may  be  due  ta 
Cu,  Sb,  or  a  rich  alloy. 

The  essentials,  in  this  scorification  process,  are: 
Heat. 

Granulated  Lead. 
Air. 


ASS  A  Y  OF  ORES  FOR  SILVER.  43 

The  accessories  are: 

Borax  glass  and  silica. 
The  variables  are: 

Borax  glass. 

Silica. 

Granulated  Lead. 

Temperature. 

Size,  depth,  and  diameter  of  scorifier. 

The  following  are  some  of  the  reactions  which  probably  take 
place  in  assaying,  for  example,  an  ore  consisting  of  PbS+Ag2S 
-f-FeS2  and  Sb2S3  in  a  silicious  (SiO2)  gangue. 

When  contents  of  scorifier  are  liquid  and  air  is  admitted  we 
have 

Pb+0       =  PbO; 


Ag2S+2PbO  =  2PbAg  (alloy)  +  SO2; 
FeS2+  sPbO  -  sPb+  FeO+  2SO2; 
Sb2S3+  pPbO  -  gPb+  Sb2O3+  3SO2; 
Sb2S3+9O      =  Sb2O3-f-3SO2; 
Sb2S3+  6PbO  =  Sb2Pb6+  3S02  ; 
SiO2+  2PbO  =  2PbO,SiO2  or  one  of  the  lead  silicates. 

Thus  we  shall  have: 

Lead  acting  as  a  collector  of  the  precious  metals,  contami- 

nated with  a  little  antimony. 
Sb2O3  and  SO2  as  volatile  substances. 
Lead  silicate,  FeO  and  Sb2O3,  as  slag-forming  material. 

If  Cu2S  were  present  in  an  ore,  we  should  probably  have  the 
following  reactions: 

2Cu2S+  ;PbO  =  2CuO+  2SO+  Pb+  CuO. 


2  2 

Part  of  the  Cu2O  would  go  into  the  slag  and  part  of  it  would 
be  reduced,  and  this  copper  would  pass  into  the  lead  button  : 

2Cu2O  +  Cu2S  =  6Cu+  SO2. 
We  might  also  have 

2CuO+  Cu2S  = 


44  NOTES  ON  ASSAYING. 

This  copper  would  make  the  lead  button  brittle  and  necessi- 
tate one  or  more  extra  scorifications. 

If  ZnS  were  present,  we  probably  should  have  the  following: 


Some  of  the  ZnO  will  volatilize  and  some  will  go  into  the  slag  or 
form  part  of  it.  A  little  will  no  doubt  be  reduced  and  pass  into 
the  lead  button: 

2ZnO  +  ZnS  -  3Zn+  SO2. 

In  order  to  avoid  a  heavy  loss  of  silver  and  gold  in  the  slag  no 
oxysulphides  should  be  present  there. 

Some  ores  require  no  addition  of  borax  glass,  others  require 
a  large  amount.  A  little  in  every  assay  does  no  harm,  but  too 
.large  an  amount  may  cover  over  the  lead  before  the  ore  is  decom- 
posed, thus  spoiling  the  assay. 

Borax  glass  acts  as  an  acid  flux  and  is  especially  useful  in  dis- 
solving and  combining  with  the  oxides  fonr  ed  during  scorification. 
The  .effect  may  be  shown  in  assaying  some  antimonial  silver 
ore.     (Mitchell's  Assaying.) 

Ore  jj  A.T.  Lead   24   grammes:    slag  carried    considerable 

silver. 

"      "       "       50        "  slag  still  carried  silver. 

"       "       "       50  and  3  grammes  of  borax 

glass  :  slag  was  free  from 
silver. 

Ores  containing  much  lime,  zinc,  and  arsenic  also  require  a 
large  amount. 

Heavily  sulphuretted  ores,  concentrates,  or  ores  deficient  in 
gangue  require  the  addition  of  silica  to  take  the  place  of  the  gangue. 
If  the  gangue  in  most  ores  is  50%  to  90%  and  jj-  A.T.  of  con- 
centra  es  with  little  or  no  gangue  is  used,  then  it  will  be  necessaiy 
to  add  from  i  to  ij  grammes  of  SiO2.  If  the  inner  surface  of 
the  scorifier  is  rough  and  much  corroded,  this  is  a  sure  indication 
.that  the  ore  is  deficient  in  gangue  and  that  silica  is  needed. 

As  a  general  thing,  the  ordinary  run   of  ores  requires  only 


ASSAY  OF  ORES  FOR  SILVER. 


45 


from  35  to  45  grammes  of  granulated  lead  to  ^  A.T.  of  ore  and 
will  be  decomposed  by  that  amount  of  lead  with  the  addition  of 
some  borax  glass.  The  following  ores,  however,  require  a  much 
larger  amount : 


Lead  required.        Heat            Borax  Glass.  Fine  SiO. 
Grammes.                                  Grammes.    Grammes. 

50-60         ^   High 

3  to  7 

60 

" 

•'< 

65 

ll 

4< 

70-QO    ^ 

Very  low 

i  to  ij 

I 

60-70    & 

" 

" 

i 

40-45  - 

Medium 

2  to  3 

70       'o 

High 

5  to  7 

I    • 

40-45  £ 

Medium 

3  to  5 

50    'g 

Low 

I  to  2 

I 

60      8 

High 

» 

i 

50    >) 

Medium 

2  to  3 

45-50 

M 

" 

60-70 

High 

" 

r 

60       J 

il 

3  to  5 

i 

Ore. 

Antimonial  ores Vio  A.T. 

Arsenical        ''     " 

Cobalt  and  nickel  ores. ...        " 

Copper  matte " 

Copper  ores    ' ' 

Galena " 

Iron  speiss %o  A.T. 

Jeweller's  sweeps " 

Lead  matte Vio  A.T. 

Lead  speiss " 

Manganiferous  ores u 

Pyrite  (FeS2) " 

Stanniferous  ores " 

Zinc  ores    ." 


Many  of  the  above,  especially  the  copper  and  nickel  ores,  will 
require  two  or  more  scorifications  before  the  lead  button  is  fit  to 
cupel. 

According  to  Karsten,  it  takes  loj  parts  of  lead  to  carry  off 
i  part  of  copper  completely.  That  is,  1.0500  grammes  of  lead 
would  be  required  to  completely  remove  .1000  grammes  of  copper. 

In  assaying  any  ore  it  is  better  for  the  student  to  use  differ- 
ent amounts  of  lead.  For  instance,  if  he  takes  three  portions  of 
the  same  ore,  he  can  use  40,  45,  and  50  grammes  of  lead  to  each 
^  A.T.  portion  of  the  ore.  If  his  results  check,  after  making, 
his  corrections  for  the  silver  in  the  lead  used,  so  much  the  better. 
If  the  highest  lead  gives  the  highest  result  or  if  the  silver  obtained 
increases  with  the  lead  used,  it  will  be  advisable  to  try  two  other 
portions  with  still  higher  lead,  for  the  ore  evidently  requires  it. 

Always  weigh  the  lead  carefully,  as  it  generally  contains  silver, 
and  a  correction  has  to  be  made  for  it  later  on  when  the  results 
are  calculated. 

The  weight  of  the  button  after  scorification  depends  upon  how 
much  gangue  the  ore  contained,  the  amount  of  lead,  borax  glass, 
and  S:O2  used, the  diameter  and  the  depth  of  the  scorifier,  and  lastly 


46  NO TES  ON  ASSAYING. 

its  position  in  the  muffle.  -  A.T.  of  one  ore  and  45  grammes  of 
lead  in  a  3"  scorifier  gave  a  resulting  lead  button  weighing  3.5 
grammes  when  the  scorifier  was  in  the  front  part  of  the  muffle  and 
5.8  grammes  when  in  the  back  part. 

The  same  ore  and  amount  of  lead  scorified  at  the  same  time 
i  i  a  scorifier  2}"  diam.  and  ij"  deep  gave  a  button  in  the  front 
of  the  muffle  weighing  18.5  grammes  and  in  the  back  of  the  muffle 
20  grammes. 

From  this  it  is  evident  that  a  3"  scorifier  is  too  broad  where 
only  45  grammes  of  lead  are  used,  for  it  is  not  always  safe  to  have 
the  resulting  lead  button  weigh  less  than  10  or  12  grammes.  It 
is  also  evident  that  it  is  possible  to  scorify  the  lead  almost  com- 
pletely away. 

Always  notice  the  color  of  the  scorifiers  after  pouring,  for  the 
silicates  and  oxides  of  the  different  metals  give  very  character- 
istic colors  and  hints  as  to  the  method  of  conducting  the  crucible 
assay,  if  the  ore  can  be  assayed  in  that  way. 

Copper  colors  the  scorifier  dark  green  to  light  green.  If 
much  iron  is  in  the  ore,  or  if  it  is  a  matte,  this  color  will  be  partly 
obscured  by  the  black  of  the  iron  oxide  in  the  first  scorification. 
The  scorifier  will  not  necessarily  be  green  if  the  ore  carries  only 
9  to  12  per  cent  of  copper  and  TV  A.T.  is  used. 

Iron  colors  the  scorifier  black  to  dark  brown.  Peroxide  of 
iron  is  yellow  or  orange. 

Cobalt  makes  the  scorifier  blue  and  gives  a  blue  slag. 

Nickel      "       "         "       black. 

Lead          "       "  lemon-yellow  to  very  light  yellow. 

Manganese  colors  the  scorifier  brownish  black  to  pink. 

Arsenic  and  Antimony,  if  present  in  large  amount,  will  leave 
crusts  on  the  inner  surface  of  scorifier  on  a  line  where  the  slag 
came  even  if  much  borax  glass  is  used. 

//  a  scorifier  is  colored  very  dark  green,  it  indicates  directly  to 
the  student  that  the  lead  button  must  contain  coppzr,  and  that  the 
button  must  be  rescorified  in  a  new  scorifier  with  or  without  an 
addition  0}  lead  in  order  to  slag  and  remove  this  impurity  (copper). 

Rescorifying  Buttons. — Buttons  weighing  over  30  grammes 
had  better  be  scorified,  whether  they  contain  impurities  or  not,  as 
they  are  rather  large  to  cupel.  Place  the  scorifier  in  the  muffle, 


ASSAY  OF  ORES  FOR  SILVER.  47 

heat  to  scorifying  temperature  (to  prevent  possible  spitting),  ard 
then  drop  in  the  lead  button;  after  it  has  been  driving  a  short  time 
add  a  little  fine  SiO2  in  order  to  save  the  scorifier.  Pb-h  O  =  PbO 
and  2PbO+SiO2  =  2PbO,SiO2.  The  slag  will  consist  of  silicate 
and  oxide  of  lead,  oxides  of  the  impurities  in  the  lead,  and  oxides 
that  have  come  from  the  scorifier.  When  impurities  like  copper 
are  present  sufficient  granulated  lead  is  added  to  bring  the  total 
weight  of  lead  in  the  scorifier  up  to  60  grammes.  The  copper  is 
oxidized  and  slagged  by  the  PbO  and  SiO2,  and  a  low  tempera- 
ture is  most  suitable  for  it.  Sometimes  a  button  requires  three 
or  more  scorifications  before  it  is  sufficiently  soft  or  pure  to  cupel. 
If  cupelled  before  this,  the  button  would  freeze  and  the  assay  be 
worthless  owing  to  the  copper. 

Keep  account  of  all  the  granulated  lead  used  in  case  there  is  a 
•correction  to  be  made  for  its  silver  contents. 

A  large  lead  button,  containing  no  impurity,  which  has  been 
scorified  to  diminish  it  in  size  is  often  brittle.  This  is  due  to 
PbO,  formed  during  the  second  scorification,  which  the  lead  has 
taken  i.p. 

Bismuth*  is  the  only  metal  that  could  be  used  to  take  the 
place  of  lead  in  the  scorification  process.  It  has  many  of  the 
characteristics  of  lead,  but  is  much  more  expensive.  Owing  to 
its  low  melting-point,  buttons  from  scorification  do  not  chill 
easily  and  much  time  must  be  allowed  for  them  to  cool  in.  In 
cupellation,  the  silver  losses  are  higher  than  when  lead  is  used, 
which  is  due  to  absorption.  On  this  account  the  cupels  should 
be  made  of  very  fine  bone-ash  and  be  very  hard.  The  "blick" 
is  not  as  distinct  as  when  lead  is  used  and  the  silver  beads  are 
often  irregular,  instead  of  being  round  and  smooth,  and  are  likely 
to  contain  bismuth.  The  color  of  the  cupel  is  very  noticeable, 
being  bright  orange-yellow  or  colored  with  alternate  rings  of 
orange-yellow  and  greenish  black. 

The  following  are  some  cupellation  experiments. 

*  Bismuth  in  cupellation ,  by  Chaudet.     Ann.  Chim.  et  de  Phys.  (3),  vol.  15, 
P.  55- 


NOTES  ON  ASSAYING. 


i 

2 

•j 

4 

B 

Bismuth    C  P     grammes  .  . 

IO   OOOO 

5  .00000 

IO  OOOOO 

Silver,           "           " 
Lead             "           " 

.2012 

.20008 
IO.OOOOO 

.20008 
5  .00000 

.20030 
IO  OOOOO 

.20030 

3    2  OOOO 

Copper         "           " 

2OOOO 

Time  of  cupellation,  minutes 
Silver  lost  in  cupelling,  per 

19 
IO.2O 

14 
2.66 

17 

Q.QI 

15 

2.14 

17 

6  23 

Silver  recovered  from  cupel, 
per  cent           .              . 

8    34. 

6    70 

i  88 

(        bend 
}  contained 

Silver  assumed  to  be  volatil- 

1.86 

VI2 

.26 

)      some 
'     copper 

Nos.  i,  2,  and  3  were  cupelled  at  one  time  and  4  and  5  at 
another.  The  high  losses  in  volatilization  shown  in  Nos.  i  and  3 
are  •  doubtless  due  to  the  presence  of  bismuth  in  the  silver  beads 
obtained  from  the  first  cupellation. 

Spitting  of  Ores  during  Scorification. — This  often  takes  place, 
but  only  during  the  first  five  or  ten  minutes  after  the  scorifiers 
have  been  placed  in  the  muffle. 

According  to  my  observation,  it  may  be  due  to  the  following 
causes : 

1.  Dampness  of  the  scorifiers. 

2.  Imperfect  mixing  of  the  charge. 

3.  Admittance  of  air  into  the  muffle  too  soon. 

4.  Insufficient  heat  when  scorifiers  are  placed  in  the  muffle. 

5.  Too  deep  a  scorifier  in  proportion  to  the  charge. 

6.  Character  of  the  ore  itself. 

Sometimes  when  a  lead  button  is  rescorified,  either  to  dimin- 
ish it  in  size  or  to  remove  impurities,  it  will  spit.  If  the  scorifier 
was  heated  before  the  lead  was  put  into  it,  the  spitting  would  not 
take  place,  which  seems  to  indicate  that  something  was  wrong 
with  the  scorifier  itself. 

Imperfect  mixing  of  the  charge,  which  is  a  cause  of  spitting 
at  times,  seems  also  to  be  one  of  the  causes  of  spitting  in  cases 
3,  4,  and  5. 

If  ore  is  left  at  the  bottom  of  a  scorifier,  it  does  not  fuse  or  get 
pasty  until  after  the  lead  has  melted  above  it.  As  this  ore  becomes 
hotter  it  swells  and  gives  off  CO2  or  other  gases,  and  as  it  swells 
and  the  gas  escapes  it  throws  up  particles  of  lead,  which  may  or 
may  not  fall  back  into  the  scorifier. 


ASSAY  OF  ORES  FOR  SILVER.  49 

Admitting  air  into  the  muffle  too  soon  will  certainly  cause 
spitting  in  many  cases,  especially  in  the  case  of  material  carrying 
much  zinc,  such  as  the  precipitates  from  the  zinc  boxes  in  the 
cyanide  process  for  treating  gold  ores. 

Some  ores  will  not  spit  under  any  circumstances,  but  if  an  ore 
tends  to  be  rather  infusible,  giving  off  much  gas  while  the  heat  is 
not  high  enough  at  first,  the  lead  will  melt  first  while  the  ore  is 
still  pasty  either  beneath  or  all  through  the  charge.  In  such 
cases  scorifiers  will  often  spit  and  soon  afterwards  a  succession 
of  small  pieces  of  ore  will  'rise  to  the  surface  and  be  oxidized  by 
the  air,  litharge,  or  both,  passing  off  to  the  circumference  and 
disappearing  in  the  slag  already  formed. 

A  deep  scorifier  is  more  liable  to  cause  trouble  than  a  shallow 
one,  because  the  lead  may  completely  cover  the  ore,  while  in  a 
shallow  one  the  ore  will  be  semi-fused  in  the  centre  and  surrounded 
by  liquid  lead. 

As  to  cause  6,  ores  such  as  AgCl,  AgBr,  and  residues  or  pre- 
cipitates like  those  just  mentioned  as  coming  from  the  zinc  boxes^ 
seem  most  liable  to  spit  in  the  scorifier,  but  the  amount  of  spitting 
can  certainly  be  diminished  by  observing  every  precaution  pos- 
sible, especially  by  using  broad  and  shallow  scorifiers  and  keeping 
the  muffle  closed  until  the  whole  contents  oj  the  scorifier  are  thoroughly 
and  completely  fused  and  liquid. 

ASSAY   OF  ZINC    RESIDUES    FROM   THE    CYANIDE    PROCESS. 
See  Assay  of  Ores  for  Gold,  page  163. 

ASSAY   OF   COPPER   MATTE   OR    COPPER   FOR  SILVER. 

This  can  be  made  in  one  of  three  ways: 

1.  By  the  ordinary  scorification  method. 

2.  By  special  scorification  method. 

3.  By  the  combination  wet  and  dry  method. 

METHOD  I.  Take  three  portions  of  ~  A.T.  of  matte  or  of 
copper,  place  in  a  3"  or  3^"  scorifier,  mix  with  35  grammes  of 
granulated  lead  and  place  35  grammes  on  top.  Add  f  to  i  gramme 
of  very  fine  silica  and  i  to  ij  grammes  of  borax  glass.  Scorify 
at  as  low  a  temperature  as  will  not  freeze  or  chill  the  assay. 


;5o  NOTES  ON  ASSAYING. 

When  the  lead  eye  covers,  pour  as  usual  and  separate  the 
lead  from  the  slag.  Weigh  each  button ;  add  sufficient  granulated 
lead  to  bring  the  total  weight  to  60  or  75  grammes  and  drop  into 
three  new  scorifiers  which  are  in  the  muffle  and  heated  to  a  scorify- 
ing temperature.  Add  about  i  gramme  of  fine  silica  and  J  gramme 
of  borax  glass  to  each,  and  scorify  again  at  a  low  temperature. 

Repeat  this  second  scorification  until  the  color  of  the  scorifier 
on  the  inner  surface  is  light  green  on  cooling.  Cupel  as  usual. 
The  color  of  the  cupel  should  be  greenish  yellow  and  not  black. 
The  latter  color,  indicates  insufficient  scorification. 

METHOD  II.  Into  3"  or  3^"  scorifiers  weigh  out  three  portions 
of  jj  A.T.  each.  Mix  with  35  to  50  grammes  of  granulated 
lead  and  spread  35  to  50  grammes  on  top.  Add  J  to  i  gramme 
of  very  fine  silica  and  i  to  ij  grammes  of  borax  glass.  Scorify 
at  as  low  a  temperature  as  possible  that  will  not  freeze  or  chill 
the  assay.  Allow  the  lead  to  slag  over  completely,  remove  the 
"scorifiers  from  the  muffle  and  pour  off  all  the  slag  possible  without 
pouring  off  any  lead.  Return  to  muffle  and  scorify  until  the 
lead  button  is  judged  to  weigh  between  8  and  12  grammes.  Re- 
move the  scorifier  and  pour  contents,  even  if  the  lead  has  not 
•slagged  over.  After  a  few  trials  the  student  will  be  able  to  judge 
the  proper  time  to  pour  and  have  the  buttons  neither  too  large 
nor  too  small.  The  scorifiers  will  be  black  or  dark  green;  if 
much  iron  is  present,  the  brown  color  will  obscure  the  green. 
'Separate  the  buttons  from  the  slag,  and  see  that  no  lead  is  in  the 
first  slag  poured  off. 

Weigh  each  button,  add  sufficient  granulated  lead  to  each  to 
bring  the  total  weight  to  75  or  90  grammes,  and  transfer  to  three 
new  scorifiers  which  are  in  the  muffle  and  heated  to  a  scorifying 
temperature.  Add  i  to  ij  grammes  of  fine  SiO2  and  J  gramme 
of  borax  glass,  and  scorify  as  before. 

If,  after  this  second  scorification,  the  scorifiers  are  very  light 
.green,  the  buttons  can  be  cupelled.  If  they  are  dark  green,  make 
a  third  scorification  as  before.  If  the  material  being  assayed  is 
of  fair  grade,  the  buttons  can  be  cupelled  separately,  but  if  of 
low  grade,  all  three  buttons  should  be  put  in  one  cupel  and  three 
more  assays  should  be  started,  if  a  check  on  the  work  is  desired. 


ASSAY  OF  ORES  FOR  SILVER. 


51 


Weigh  the  buttons,  part  for  gold,  and  deduct  the  amount  found 
from  the  original  weight  of  the  button  or  buttons. 

Experiments  carried  out  by  Mr.  H.  T.  Graber,  class  of  1903, 
upon  a  copper  matte  show  the  following  interesting  data  in 
regard  to  the  removal  of  the  copper  and  the  influence  thereon  of 
borax  glass,  silica,  ordinary  glass,  and  borax  glass  and  silica 
together. 


FIRST  SCORIFICATION. 

No. 

Weight 
of  Matte 
Taken. 

Lead 
Taken 
($  mixed 
with 
Matte,  ^ 
on  Top) 
Grms. 

Ratio  of 
Pb  to  Cu 

in 
A  A.T. 

of  Matte. 

Ordi- 
nary 
Glass. 

Silica 
(very 
fine), 
Grms. 

Weight 
of  Lead 
Button. 

Copper  in  TV  A.T. 
Matte  =  1.5  84 
Grammes. 

Weight 
of 
Copper 
Removed 

Per  cent 
of  Copper 
Removed 

in  Slag. 

in  Slag. 

i  ' 

TV  A.T. 

50 

31  to  i 

Pinch 

i 

15 

.7851 

49.6 

2 

'  ' 

' 

* 

13 

I.OOOO 

63-1 

3 

" 

' 

• 

12 

•6597 

41.6 

4 

A 

" 

' 

1 

9 

.9910 

62.5 

5 

" 

' 

1 

9 

.8773 

55-4 

<> 

M 

1 

1 

15 

•55941     35-3 

7 

'  ' 

1 

1 

15 

•5963 

37-6 

«< 

it 

' 

1 

9 

1.0163 

64.2 

Borax 

Glass. 

t 

^ 

&A.T. 

50 

31  to  i 

Pinch 

t 

10 

i  .0114 

63.8 

2 

" 

1 

ii 

•8549      53-9 

3 

'  ' 

' 

1 

7-5 

.9626 

60.7 

4 

" 

' 

1 

7-5 

i  .  0999 

69.4 

5 

>B 

" 

* 

9 

**ii3i 

65-3 

-6 

* 

ii 

.8808 

55-6 

7 

" 

' 

' 

9 

.9182 

57-9 

3 

'  ' 

< 

' 

9 

1.1150 

70.4 

9 

J 

i 

* 

8 

i  .  2551 

79-2 

10  4 

6 

1.2577 

79-4 

i  "1 

TV  A.T. 

50 

31  to  i 

3 

none 

10 

.8864 

55-9 

3JC 

<  t 

t  t 

tt 

3 

H 

8 
ii 

•9534 
•65°5 

60.2 
41.  x 

4] 

1  1 

8 

.8072 

50-9 

l\ 

iVA.T. 

50 

31  to  i 

none 

3 

6 

i  .  1384 

71.9 

<UD 

'  ' 

f  t 

'  ' 

'  ' 

7 

•9574 

60.5 

7 

'  ' 

'  ' 

i  c 

1  1 

" 

6 

1-035°     65-3 

8J 

1  1 

7 

i.  1165!     70.5 

*  To  make  total  lead  60  grammes  at  the  beginning  of  second  scorification. 
r  To  make  total  lead  35  grammes  at  the  beginning  of  second  scorification. 
t  To  make  total  lead  up  to  45  grammes  in  the  third  scorification. 


NOTES  ON  ASSAY  WG. 


The  matte  carried  54.3%  copper, 
25  oz.    gold, 
45  oz.    silver. 

The  work  was  done  in  a  muffle  fired  with  gas,  and  shallow 
3"  scorifiers  were  used  in  all  assays. 

In  looking  over  this  table  it  is  evident  that  from  60%  to  70% 
of  the  copper  present  is  removed  during  the  first  scorification 


No. 

SECOND  SCORIFICATION. 

THIRD  SCORIFICATION. 

Per 

Silica 
Added, 
Grms. 

ead  Added. 

Ratio  of 
Pb  to  Cu 
Remain- 
ing in 
Button. 

Per 
Cent  of 
Copper 

moved. 

Cent 
of  the 
Orig- 
inal 
Copper 
Pres- 

Silica 
Added. 

Lead 
Added. 

Ratio  of 
PbtoCu 
Remain- 
ing. 

Per 
Cent 
of  Cu 
Re- 
moved. 

Per 
Cent  of 
Orig- 
inal. 

Weight 
of  Final 
Lead 

Button, 

£ 

ent. 

I 

,1 

45* 

75  to 

53-5 

26.9 

2 

47* 

126  to 

67-4 

24.8 

none 

as* 

140  to  i 

94.0 

H-3 

10 

3 

48* 

64  to 

47.8 

27.9 

4 

A 

5i* 

101  to 

58.8 

22.  O 

none 

25t 

100  to  i 

45-1 

6.9 

4 

5 

51* 

84  to 

49-9 

22.5 

6 

45* 

58  to 

5*-7 

33-5 

7 

2of 

60  to 

46.3 

28.8 

8. 

26f 

105  to 

49.8 

17.8 

l\ 

1 

If 

i 

24* 

24  to  i 

42.3 

16.1 

none 

25§ 

24  to  i 

15.2 

3-32 

8 

Si 

>B 

6 

7 

i 

i 

22* 

25  to  i 

47-5 

17.9 

none 

25§ 

24  to  i 

29.2 

5-78 

8 

8. 

9 

i 

art 

106  to  i 

60.2 

12.5 

10 

- 

29f 

107  to  i 

28.8 

5-9 

»Sfi 

150  to  i 

13-9 

2.1 

10 

Tl 

1 

Borax 

Neither 

Glass 

Borax 

2 

3 

>C 

3 

23* 

20  tO  I 

31.0 

*5«* 

Glass 
nor 

2511 

17  to  i 

IO.I 

3-3 

IO 

4. 

Silica. 

11 

Silica. 

*\ 

D 

3 

34* 

28  to  i 

37-8 

12.5 

No 

25li 

27  to  i 

4.0 

•83 

ij 

Silica. 

§  Total  lead  was  33  grammes  at  the  beginning  of  third  scorification. 
1  To  make  the  total  35  grammes. 


ASSAY  OF  ORES  FOR  SILVER. 


53 


and  from  50%  to  60%  of  the  remainder  during  the  second 
scorification. 

Silica  evidently  effects  the  slagging  of  the  copper  faster  than 
borax  glass,  but  a  little  of  each  in  the  first  scorification  seems  to 
be  most  satisfactory;  after  that  silica  alone  will  do,  although 
a  little  borax  glass  in  addition  does  no  harm.  The  ratio  of  the 
lead  to  the  copper  has  a  great  influence  on  the  amount  of  copper 
slagged,  and  the  greater  the  ratio  the  more  copper  seems  to  slag. 
For  this  reason  it  seems  advisable  to  use  70  or  more  grammes 
at  first,  and  when  four  buttons  from  the  first  scorification  are 
combined,  to  make  the  total  lead  up  to  75  or  100  grammes  rather 
than  sixty. 

Metallic  Copper,  Copper  Bars,  etc. — Assay  as  in  the  case  of 
mattes,  Method  II.  -^  A.T.  may  be  used,  but  it  is  generally 
better  to  take  -^  A.T.,  unless  the  material  carries  very  little 
silver. 

The  following  is  an  example  of  Method  II. 


COPPER  DRILLINGS. 
Scorifiers  T&". 


&A.T. 

Borax  glass.  .    i  gramme 
Gran.  lead...  70  grammes 


SiO, 


i  gramme 


A    A.T. 
i  gramme 
70  grammes 
i  gramme 

&A.T. 

i  gramme 
100  grammes 
i  gramme 

&  A.T. 
I  gramme 
100  grammes 
i  gramme 

Scorified  and  poured  slag  off  once. 
Placed   again  in  muffle,  scorified 

and  poured. 
Lead  button..  6  6  grammes 

Lead  added 68 

Total  lead  ....   80  grammes 
Scorified  as  before  with  borax  glass 

and  SiO2. 

Lead  button ....    12 
Lead  added 58  grammes 

Total 70  grammes 

Scorified  as  before. 
Lead  button  ....   13  grammes. 
Cupelled  with  feather  litharge  crystals. 
Ag-f  Au  =  .  04430  grammes 


Scorified  and  poured  slag  off  twice. 


8  grammes 

» 

70  grammes 

90  grammes. 

Scorified  as  before  with  borax  glass 
and  SiO2  and  poured  slag  off  twice. 
9  grammes. 

Cupelled  with  feather  litharge  crys- 
tals. 
Ag+Au  =  0.4454  grammes. 

=  222.7  oz- 

This  cupel,  owing  to  only  two  scori- 
fications,  showed  a  little  more  coppei 
oxide  than  the  other. 


54  NOTES  ON  ASSAYING. 

In  the  scorification  of  copper  ores  or  any  cupriferous  material 
I  advise  the  continuation  of  the  process  until  the  scorifier  is- 
light  green,  for  this  color  indicates  that  there  is  only  a  small 
amount  of  copper  left  in  the  lead  and  the  cupels  will  be  but 
slightly  colored  with  the  black  oxide  of  copper.  I  know,  however, 
that  lead  buttons  full  of  copper  are  often  cupelled,  and  if  the 
silver  beads  blick,  the  assays  are  considered  all  right.  This  of 
course  may  save  one  scorification,  but  the  cupels  full  of  black 
oxide  of  copper  are  liable  to  carry  much  silver. 

Some  assayers  claim  that,  in  assaying  mattes  and  copper 
ores,  the  temperature  should  be  extremely  high  when  the  scorifier 
is  first  placed  in  the  muffle,  and  then  dropped  to  a  very  low  tem- 
perature, as  soon  as  the  lead  commences  to  "  drive  "  and  kept  so 
during  scorification. 

Silver  in  matte,  copper  and  copper  bars  is  paid  for  on  the 
basis  of  95%  of  silver  contents,  and  the  price  is  that  quoted  on 
the  day  after  the  agreement  of  the  assays. 

Combination  Wet  and  Dry  Methods.  —  There  are  several 
of  these  methods,  and  they  generally  give  higher  results  for  silver 
than  the  all- scorification  methods.  This  no  doubt  partly  accounts 
for  the  lack  of  uniformity  of  results  by  different  assayers,  and  it 
seems  only  right,  if  umpire  work  is  being  done  and  assayers 
are  checking  each  other,  that  the  method  used  should  be  the 
same  for  one  and  all. 

The  following  method  is  one  given  by  W.  R.  Van  Liew  in. 
Eng.  and  Mining  Jour.,  April  21,  1900: 

"Take  two  or  three  portions  of  i  A.T.  each,  place  in  beakers,, 
add  200  c.c.  of  cold  water  and  100  c.c.  of  HNO3  (sp.  gr.  1.42). 
After  a  short  period  of  action  the  beakers  are  placed  on  a  steam- 
plate,  and  by  the  time  the  temperature  has  reached  its  maxi- 
mum (80°  C.)  the  copper  is  mostly  dissolved.  At  the  end  of 
one  hour  complete  solution  has  resulted,  and  at  the  end  of  2^ 
hours  the  beakers  are  removed,  cooled,  and  2  to  3  c.c.  of  normal 
salt  solution,  exceeding  that  amount  necessary  to  precipitate  all 
the  silver  present,  are  added,  and  the  next  morning  the  precipi- 
tate of  AgCl  is  filtered  into  a  double  No.  o  i5-cm.  MunktelPs 
Swedish  filter-paper.  Be  sure  and  wash  all  the  AgCl  to  the 


ASSAY  OF  ORES  FOR  SILVER.  5S 

extreme  point  of  the  filters.  The  wet  papers  are  then  place u 
in  2j-inch  scorifiers  containing,  approximately,  6  grammes  of  test 
lead  in  their  bottoms  and  burned  to  complete  ash  in  a  muffle 
not  yet  at  incipient  redness.  The  carbon  burnt  off,  they  are 
removed,  when  more  test  lead,  litharge,  and  borax  are  added 
and  the  scorifiers  replaced  in  the  muffle.  They  are  scorified 
at  a  low  heat  for  approximately  20  minutes  or  until  the  lead  but- 
tons weigh  some  4  grammes.  These  resulting  lead  buttons  are 
then  cupelled  at  a  temperature  giving  heavy  litharge  crystals. 
The  time  of  operation  is  24  hours."  * 

If  gold  is  present  in  the  copper  bars  or  drillings,  the  method 
is  conducted  as  per  page  181,  the  resulting  silver  and  gold  bead 
is  weighed,  parted,  and  the  amount  of  gold  allowed  for. 
Copper  Mattes — Crucible  Fusion.     (See  page  118.) 

CUPELLATION. 

The  lead  button  from  any  scorification,  which  should  be* 
soft,  malleable,  and  in  the  form  of  a  cube  with  truncated  edges 
and  corners,  weighing  not  over  30  grammes,  is  now  ready  for 
cupelling.  This  lead  button  should  contain  all  the  gold  and 
silver  in  the  ore  and  members  of  the  platinum  group,  and  our 
next  step  is  to  oxidize  this  lead  to  litharge,  which  is  absorbed  by 
the  cupel,  leaving  the  gold  and  silver  and  members  of  the  platinum, 
group,  as  a  small  bead,  on  the  cupel.  //  is  safe  to  warm  the 
cupels  on  top  0}  the  jurnace  and  later  on  gradually  push  them 
into  the  muffle,  heated  to  the  full  temperature.  This  gradual 
heating  may  prevent  cracking.  When  heated  red  all  through 
the  lead  buttons  are  carefully  dropped  into  them,  while  they  are* 
in  the  jurnace,  the  front  cupels  being  charged  first.  If  the  cupels 

*  References  to  assay  of  copper-material : 

A.I.M.E.,  vol.  24,  p.  575.  A.  R.  Ledoux. 

"  "    25,  p.  250,  1000.  "     " 

"  "    30,  p.  529.  L.  D.  Godshall. 

"      30,  p.   II2I. 

Eng.    &  Min.  Jour.,  vol.  65,  p.  223. 

"       "      "          "        "    69,  p.  469.     W.  R.  VanLiew. 

"       "      "          "       "    74,  p.  650.     T.  B.  Swift. 
Jour,  of  Analyt.  Chem.,  vol.  6,  p.  262.     Prof.  Whitehead. 


56  NOTES  ON  ASSAYING. 

are  thoroughly  dry  or  warm,  they  can  be  placed  directly  in  the 
hot  muffle. 

Be  sure  that  the  cupel  weighs  more  than  the  lead  button  and 
that  the  bowl  will  contain  the  lead  without  overflowing. 

The  door  of  the  muffle  is  now  closed  and  the  buttons  fused 
as  quickly  as  possible.  When  this  is  accomplished  and  the 
PbO  begins  to  form,  i.e.,  when  the  buttons  have  cleared  or  begin 
to  "drive,"  the  door  of  the  muffle  is  opened  and  the  temperature 
lowered.  Make  note  of  the  time.  The  heat  should  be  kept 
much  lower  than  in  scorification.  //  it  is  exactly  right  (625° 
to  775°  C.),  crystals  of  PbO  will  be  seen  forming  all  around  the 
inner  surface  of  the  cupel  or  on  the  front  or  cooler  side,  just  above 
the  button. 

If  the  heat  is  too  high,  no  crystals  of  litharge  will  form,  the 
whole  cupel  looks  very  hot,  and  the  color  of  the  litharge,  absorbed 
by  the  cupels,  is  very  indistinct. 

Above  775°  C.  silver  will  volatilize  rapidly.  (At  925°  the 
loss  is  3%  to  4%,  and  at  1000°  C.  over  4%.)  If  the  heat  is  too 
low,  the  cupels  appear  dark  and  cold;  a  film  of  litharge  begins 
to  form  over  the  button  of  lead;  it  ceases  "to  drive";  then 
"freezes,"  and  the  assay  is  rendered  worthless. 

The  lead  button  is  now  gradually  oxidized  by  the  air,  most 
of  the  litharge,  i.e.,  90%  to  95%,  being  absorbed  as  such  by 
the  cupel;  the  remainder  going  off  as  oxide  (PbO),  which  is 
later  on  changed  to  carbonate  of  lead  by  the  excess  of  air. 
As  the  button  grows  smaller  it  will  be  noticed  that  ft  becomes 
more  round  and  that  the  beads  or  drops  of  litharge,  which  are 
continually  thrown  from  the  centre  of  the  button  towards  the 
circumference  become  larger  and  appear  like  drops  of  oil  upon 
water.  This  indicates  that  the  button  is  near  "blicking"  or 
< 'brightening,"  and  the  heat  should  be  slightly  raised  or  the  cupel 
pushed  back  into  the  hotter  part  of  the  furnace.  As  the  last  of 
the  litharge  goes  off  the  button,  one  will  notice  a  brilliant  play  of 
colors  and  the  button  seems  to  be  agitated  and  revolving  upon  an 
axis.  As  the  last  of  the  colors  disappear,  the  button  becomes  dull 
and  after  a  second  or  so  looks  bright  and  silvery.  Again  make 
note  of  the  time  and  see  how  much  lead  has  oxidized  per  minute 


ASSAY  OF  ORES  FOR  SILVER.  57 

during  cupellation.     This  last  part  of  the  cupelling  process  is 
called  the  "  brightening "  or  "blicking." 

The  cupel  should  be  immediately  drawn  out  from  the  muffle 
far  enough  to  have  the  button  solidify.  When  the  button  solidi- 
fies it  will  again  flash  or  glow.  Good  buttons  should  separate 
easily  from  the  cupel,  have  a  silvery  lustre  or  surface,  be  round 
if  small  and  hemispherical  if  large,  dullish  white  upon  the  bot- 
tom, and  have  no  rootlets.  Large  buttons  should  be  withdrawn 
"very  slowly  or  else  covered  over  with  a  hot  cupel;  otherwise  they 
will  "sprout"  or  "vegetate" 

Silver  buttons  containing  much  gold  seldom,  if  ever,  sprout. 

Sprouting  is  said  to  be  due  to  the  button  suddenly  giving 
off  the  oxygen  which  it  has  absorbed  during  the  cupelling  process. 

Sprouted  buttons  as  well  as  those  which  have  jrozen  should  be 
rejected,  as  they  generally  give  low  results  even  if  brought  again 
to  "  driving  "  by  the  addition  of  fresh  lead  or  charcoal  or  both. 
A  cupel,  provided  the  bowl  is  large  enough,  will  absorb  about  its 
own  weight  of  litharge,  and  the  different  oxides  absorbed  color  it 
as  follows: 

Lead  colors  it  yellow;  copper,  black  to  greenish  black; 
iron,  black  and  leaves  a  black  scoria  on  the  sides.  Zinc  causes 
boiling  and  will,  if  present  in  large  amount,  crack  the  cupel. 
Antimony  cracks  the  cupel  to  pieces  if  present  in  large  amount; 
if  present  only  in  small  amount,  it  will  simply  cause  a  roughening 
of  the  edges  of  the  cupel.  Rings  of  light-colored  scoria  may  be 
due  to  the  oxides  of  arsenic,  antimony,  zinc,  or  tin. 

Nickel,  if  present  above  J%,  will  leave  a  blackish-green  scum 
of  nickel  protoxide.  The  button  will  "drive"  at  first,  but  will 
finally  leave  the  scum  all  over  the  cupel.  The  lead  goes  into 
the  cupel  as  PbO  as  usual.  Under  J%  of  nickel  the  lead  button 
will  cupel,  but  a  green  coating  is  generally  left  upon  the  cupel. 

The  heat  in  cupelling  should  always  be  lower  than  in  scorifying^ 
but  should,  especially  in  the  case  of  large  beads  or  of  gold  buttons, 
be  raised  at  the  period  of  "blicking,"  in  order  to  keep  the  silver 
or  gold  melted  while  the  last  traces  of  lead  and  litharge  in  the 
button  are  being  removed. 

When  the  bead  is  perfectly  cold  it  is  seized  by  the  button- 


58  NOTES  ON  ASSAYING. 

pincers,  detached  from  the  cupel,  to  which  it  should  adhere  only 

slightly,    and  brushed  with  a   stiff  brush.     If   this 

does  not  clean  it  thoroughly,  it  should  be  placed 

upon  its  side  on  a  small   anvil,    hammered,  and 

then  brushed  again.     The  button,  which  must  be  perjectly  coldy 

is  now  ready  to  be  weighed. 

The  balance  upon  which  this  is  done  should  be  sensitive 
to  T^O-  of  a  milligramme.  Such  balances  should  be  handled  with 
the  utmost  care  and  should  be  in  perfect  adjustment  before  any 
weighing  is  attempted.  All  buttons  should  be  weighed  to  the 
fifth  place  of  decimals  (thus:  .05063  grammes),  and  should  be 
reported  in  ounces  and  fractions  thereof  (thus:  60.3  oz.). 

EXAMPLE. 

No.  i.  'No.  2. 

Weight  of  ore  taken ^  A.T.  -» 2 .9166  grammes  ^  A.T. 

Lead  used 35  45  grammes. 

Weight  of  Ag+ Au  obtained 00632         "  .00640         " 

Silver  contained  in  the  Pb  used 00029         "  .00037         " 


Weight  of  Ag+ Au  in  ore 00603         "  .00603         *' 

Ounces  per  ton 60 . 3  60 . 3 

Value  at  market  rate,  say  5oc.  =$30. 15  per  ton  of  2000  Ibs. 

"  Control  "  or  "  check  "  assays  are  generally  done  in  triplicate- 
If  two  results  agree,  the  third  is  discarded;  if  all  three  disagree,  the 
ore  is  again  assayed.  "  Umpire  "  work  often  necessitates  six  assays. 

The  chief  loss  in  the  silver  assay  occurs  during  cupellation. 

The  lead  buttons  should  really  be  free  from  impurities  of  all 
kinds,  but  in  reality  they  generally  contain  some.  For  example, 
suppose  we  take  the  lead  buttons  from  the  ores  previously  scorified 
(see  page  43) ;  some  of  the  reactions  which  probably  take  place 
in  cupelling  are  as  follows: 

The  button  is  lead  carrying  Au,  Ag,  and  a  very  little  Sb,  Zn> 
and  Cu  as  impurities.  We  admit  air  into  the  mufHe  when 
we  are  cupelling  this  button,  and  we  have  Pb+O  =  PbO,  which 
is  partly  absorbed  by  the  cupel  and  partly  volatilized;  as  this 
PbO  comes  in  contact  with  the  air,  it  is  converted  into  lead 
carbonate  and  coats  the  furnace  white  outside  the  muffle. 

The  Sb2O3  is  partly  volatilized  and  partly  carried  into  the 
cupel  along  with  the  PbO: 


ASSAY  OF  ORES  FOR  SILVER. 


59 


2Sb+ 30  =  Sb203 ;     2Sb+ 3PbO  =  Sb2O3 
TheZnO  is  partly  carried  into  the  cupel  and  partly  volatilized: 

Zn  +  O  =  ZnO;    Zn-j-PbO  =  ZnO  +  Pb. 

If  much  zinc  is  present,  it  will  burn  and  oxidize,  giving  off  a 
very  brilliant  greenish-white  flame. 

The  CuO  is  absorbed  by  the  cupel  and  colors  it  black: 

Cu+O  =  CuO;    Cu+PbO  =  CuO+Pb. 

The  Ag  and  Au  are  not  oxidized,  but  are  left  on  the  cupel  with 
the  exception  of  a  very  small  amount,  which  is  partly  carried  into 
the  cupel  by  the  PbO  and  partly  volatilized  with  the  PbO.  These 
losses  are  dependent  largely  upon  the  heat  used,  the  texture  of 
the  cupel  itself,  and  the  size  of  the  lead  button. 

The  following  will  give  some  idea  of  what  becomes  of  the 
lead  during  the  cupellation  process: 


Pb°  Absorbed  ^  CuPel« 


Percentage  of  Pb 


'30.  2  grammes          30.9    grammes  =28.  67  Pb          94-9 

28.6 

29.2 

=  27.10 

94.8 

No  feather  crystals 
of    PbO     upon  . 
cupels. 

28.4 
28.2 
16.0 

28.8 
28.7 
16.4 

=  26.73 
=  26.64 
=  15.22 

94.1 
94-4 

15.3 

iS-7 

=  14-57 

95-2 

14.9 

15.2 

=  14.18 

95-2 

i3-3 

13-5 

=  12.52 

94.2 

36.0 

37-5 

=  34.80 

96.0 

In  the  last  the  cupel  weighed  31  grammes  when  new;  after 
use  it  was  completely  full  of  PbO  and  weighed  68J  grammes. 

The  principal  loss  in  the  silver  assay  occurs  in  cupelling;  part 
of  this  loss  is  due  to  volatilization,  but  the  chief  source  of  error 
is  occasioned  by  absorption  of  the  silver  by  the  cupel.  This  is 
easily  shown  by  taking  a  known  weight  of  silver-foil  (C.P.), 
wrapping  it  up  in  some  C.P.  lead-foil,  and  carefully  cupelling  it. 

Experiment  with  C.P.  Silver. — Weigh  out  accurately  upon 
the  button-balance  one  portion  of  C.P.  silver-foil,  from  .2  to  .4 
of  a  gramme,  say  .29918  grammes. 


^0  NOTES  ON  ASSAYING. 

Weigh  out  between  6  and  7  grammes  of  C.P.  lead-foil  upon 
the  pulp-balances. 

Wrap  the  C.P.  silver  in  the  C.P.  lead. 

Weigh  a  cupel  from  which  the  bone-ash  does  not  rub  off 
easily  and  heat  to  cupelling  temperature. 

Drop  the  button  of  lead  and  silver  into  the  cupel. 

Cupel  with  feather  litharge  crystals.  Note  the  time  from  the 
•driving  to  the  blicking  of  the  button.  Have  a  hot  cupel  at  hand 
to  cover  the  one  in  use  when  the  button  blicks.  Remove,  clean, 
.and  then  weigh  silver  button  and  weigh  cupel  again. 

Now  take  the  cupel,  cut  off  all  the  bone-ash  not  colored  with 
PbO,  and  grind  the  remainder  through  a  6o-mesh  sieve.  Weigh. 
Assay  for  silver  by  the  crucible  method,  using  50  PbO,  20  borax, 
5  silica,  and  2j  argols,  or  60  PbO,  10  borax  glass,  5  silica,  15  soda, 
and  2j  argols  (R.P.  =  10).  These  charges  will  do  when  the 
'weight  of  bone-ash  plus  PbO,  minus  the  actual  weight  of  litharge, 
<ioes  not  exceed  15  to  20  grammes;  above  this  the  lithaige, 
silica,  and  especially  the  borax  glass  will  have  to  be  increased. 
Cupel  the  resulting  lead  button.  Weigh  the  silver  bead  and 
deduct  the  silver  in  the  PbO  used,  if  any  is  present. 

Report  as  follows: 

Weight  of  C.P.  silver  taken,  for  instance .  29918  grammes 

"       "     "       "      after  cupellation 29590 


Silver  lost  during  cupellation 00328  =  1.09% 

Weight  of  silver  found  in  cupel,  less  correction 

for  Ag  in  PbO  used 00288 

Percentage  of  silver  absorbed  by  the  cupel 96 

"          "      "      lost  by  volatilization 13 

Weight  of  C.P.  lead  taken 6.00  grammes 

"  cupel+PbO 27.95 

"  cupel  before  using 21 .81 

Weight  of  PbO 6.14 

Weight  of   lead   calculated   from   the   PbO  =  5. 69   grammes. 

From  the  PbO  absorbed,  calculate  the  per  cent  of  the  original 
lead  that  is  in  the  cupel  =  94.83%. 


ASSAY  OF  ORES  FOR  SILVER.  61 

If  the  silver  button  recovered  from  the  cupel,  less  any  silver 
in  th  litharge  used  (.00288  grammes),  is  more  than  is  indicated 
by  the  loss  in  cupelling  (.00328),  that  is,  if  in  the  foregoing  test 
the  weight  .00288  grammes  had  come  out  .00342  grammes  then 
there  must  have  been  lead  either  in  .29590  grammes,  making 
the  loss  (.00328)  too  small,  or  else  there  was  lead  in  .00342 
grammes. 

Such  a  result  may  occur  if  the  cupel  is  not  pushed  back  into 
the  hotter  part  of  the  furnace  just  before  the  button  blicks. 

It  is  seen  from  this  experiment  that  the  resulting  silver  button 
weighs  considerably  less  than  the  amount  of  silver  originally 
taken,  and  that  about  90  per  cent  of  this  loss  is  due  to  absorp- 
tion by  the  cupel. 

This  loss  is  influenced  by: 

1.  The  cupel,  whether  hard  or  soft.    A  hard  cupel  may  not 
absorb  the  PbO  as  fast  as  made,  thus  prolonging  the  operation; 
and  increasing  the  loss  of  silver.    A  cupel  may  be  so  soft  that 
the  PbO  will  carry  silver  into  it. 

2.  The  character  and  fineness  of  the  bone- ash  of  which  the 
cupel  was  made. 

3.  The  amount  of  silver  cupelled.     The  larger  the  amount 
of  silver  cupelled  the  greater  is  the  loss  of  silver,  but  the  smaller 
is  the  percentage  loss. 

4.  The  amount  of  lead  used.     Beyond  a  certain  size  of  but- 
ton the  loss  of  silver  will  increase  because  the  time  of  cupellation 
will  be  unnecessarily  prolonged. 

5.  The  presence  of  base  metals  in  the  button.    If  a  button 
contains  much  copper,  CuO  will  be  formed  with  the  PbO  and 
this,  when  absorbed  by  the  cupel,  seems  to  drag  silver  with  it 
into  the  cupel.    The  presence  of  Sb  will  increase  the  loss  of 
silver  both  by  absorption  and  volatilization. 

6.  The   temperature   at  which   the   cupelling  is  carried  on. 
Feather  crystals  of  litharge  should  appear  on  the  inner  surface 
of  the  cupel,  usually  in  front,  otherwise  the  temperature  is  toe* 
high. 

7.  The  quantity  of  air  passing  into  or  through   the  muffle. 


62 


NOTES  ON  ASSAYING. 


Too  little  air  delays  the  operation,  causing  loss;    too  much  air 
may  make  the  operation  too  rapid. 

The  following  tables  are  taken  from  the  thesis  of  Messrs.  F. 
J.  Eager  and  W.  W.  Welch,  class  of  1902,  who  investigated  these 
losses.  They  used  a  gas-muffle,  made  their  own  cupels,  and  a 
sample  of  the  bone-ash  they  used  sized  as  follows  : 

On  2o-mesh  sieve  ...........................    2  .  10% 

Through    20  on  40  .........................     i  .  oo 

40  "  60  .........................     3.00 

60  "  80  .........................     5.20 

80  "  100  ........................  13.00 


"  120  ..............................    68.20 

This  bone-ash  required  only  10%  of  water  to  make  it  of  the 
eight  consistency  before  pressing  it  in  the  cupel-machine. 

SILVER  LOSSES  IN  CUPELLATION. 

The  following  table  shows   the  importance  of  cupelling   at 
the  correct  temperature. 

Lead  and  silver  constant,  temperature  varying. 


C.P.  Silver 
used  in 
Grammes. 

Lead. 

Time, 
Minutes. 

Temp. 
C. 

Per- 
centage 
Loss. 

Remarks. 

.  20462 
.  20606 

10  grammes 

15  to  18 

« 

700° 

•99 
1.05 

)  Crystals  of  PbO 
>•      all  about  the 
)      button. 

.20427 

15 

775 

1.18 

Crystals  of  PbO 

.20010 

16 

.76 

>      on  cooler  side 

.20472 

'Si 

1  1 

.41 

)      of  cupel. 

.20554 

i6J 

850 

.70 

No  more  crystals. 

.  20030 

15 

" 

.81 

.20140 

15 

11 

.69 

.20518 

Not  taken 

850 

•75 

.20016 

<(       « 

to 

.69 

.  20300 

«       <( 

870 

.80 

.20172 

ii 

925 

2*59 

.  20380 

10 

<  « 

3-53 

.20347 

ii 

n 

3.78 

.20129 

14* 

1000 

4.78 

.20586 

*5 

<« 

4-97 

ASSAY  OF  ORES  FOR  SILVER.  63^ 

The  temperatures  were  taken  by  a  Le  Chatelier  pyrometer, 
and  as  the  junction  could  not  be  held  in  the  lead  button,  it  was 
kept  about  J"  above  it. 

It  was  found  that  the  temperature  there  was  about  100° 
higher  than  above  the  floor  of  the  muffle  at  the  same  spot,  due 
no  doubt  to  the  oxidation  of  the  lead  itself.  This  explains  why 
buttons  can  be  cupelled  at  a  comparatively  low  temperature 
after  they  have  started  to  drive.  In  order  to  give  a  quick  drive 
the  buttons  were  melted  at  775°;  the  temperature  could  then  be 
lowered  to  625°  and  the  buttons  kept  driving,  but  towards  the 
"  blick"  the  temperature  had  to  be  raised  to  750°  or  775°.  To 
cupel  at  as  low  a  temperature  as  625°  can  be  done  even  in 
practice,  but  it  requires  care  and  attention.  At  this  temper- 
ature crystals  of  litharge  form  all  about  the  button.  The  range  for 
these  crystals  seems  to  be  from  625°  C.  to  about  800°  or  825°. 
The  temperature  of  the  muffle  varied  about  400°  from  the  front 
to  the  back.  Looking  at  the  table,  it  is  seen  that  the  silver  loss 
increases  rapidly  as  soon  as  no  more  crystals  are  obtained  on  the 
cupel,  and  it  is  for  this  reason  that  the  cupelling  temperature 
should  always  be  sufficiently  low  to  obtain  these  crystals.  The 
cupels  should,  however,  always  be  pushed  back  into  the  hotter 
part  of  the  furnace  just  before  the  button  blicks,  otherwise  it 
will  be  apt  to  carry  leaot. 

Another  thing  noticed  in  this  run  was,  that  as  the  temperature 
increased  the  tendency  of  the  buttons  to  sprout  increased.  At 
1075°  it  was  almost  impossible  to  keep  them  from  sprouting. 
Furthermore,  as  the  loss  increased,  the  color  of  the  cupels,  where 
soaked  with  litharge,  became  more  green,  which  was  evidently 
due  to  the  increased  amount  of  silver  absorbed. 

The  following  table  shows  the  effect  of  varying  the  amount 
of  lead. 

Silver  and  temperature  constant. 

Three  determinations  were  made  at  one  time,  and  all  condi- 
tions were  kept  as  nearly  alike  as  possible. 


64 


NOTES  ON  ASSAYING. 


No. 

Silver. 

Lead. 

Temp. 
C. 

Percentage 
Loss. 

Mean  of  the 
Two  Nearest 
Together. 

f    I 

.20517 

10  grammes 

685° 

fi-35 

\     2 

.20168 

«« 

« 

\  i  70 

1  .  30 

1    3 

.  20404 

1  1 

« 

li-42 

1! 

•2°555 
.20651 
.20077 

a 

H 
r< 

f  i  30 

jili 

1.38 

r  7 

.20182 

20 

" 

fi.49 

8 

.20284 

11 

M 

I.»5 

1.52 

1    9 

.20318 

** 

(4 

Li-55 

fio 
11 

[  12 

.20225 
.20517 
.  20632 

25 

» 

fl.82 

\  1.87 

[1.22 

I.8S 

The  table  below  shows  the  effect  of  varying  the  amount  of 
copper. 

Silver,  lead,  and  temperature  constant. 


No. 

Silver. 

Lead, 
Grammes. 

Temp. 
C. 

Copper. 
Per  Cent  of 
the  Silver. 

Percentage 
Loss. 

Mean  of  the 
Two  Nearest 
Together. 

i 

.  20382 

IO 

775° 

5 

{I  .OO 

2 

.20256 

I.  10 

1.05 

3 

.20036 

c  « 

.90 

4 

.  20618 

IO 

f      .19. 

I 

.20193 
.20118 

tt 

i  ( 

\     .09 
(    .06 

1.  08 

7 

.20146 

IS 

•  27 

8 

.20138 

<  < 

\  .30 

1.29 

9 

.  20432 

tt 

1    -35 

10 

.20282 

20 

•I5 

ii 

.2OIOO 

'  ' 

\     -45 

1-45 

12 

.  20338 

" 

I    .46 

13 

.20224 

25 

f  *-05 

(Copper     in- 

14 

.  20496 

<  < 

•95 

the  silver 

15 

.  20420 

1  1 

I  i-°7 

buttons. 

Many  things  worthy  of  note  were  observed  in  this  series. 
The  presence  of  copper  made  it  necessary  to  have  the  tempera- 
ture of  the  muffle  900°  in  order  to  make  the  lead  drive.  The 
temperature  was  then  lowered  to  775°.  The  presence  of  5%  and 
10%  of  copper  seemed  to  have  very  little  influence  on  the  loss  of 
silver,  but  it  is  to  be  remembered  that  the  ratio  of  lead  to  copper 
is  over  400  to  i. 

Above  10%  copper  the  silver  loss  increased,  and  when  25%, 


ASSAY  OF  ORES  FOR  SILVER.  65 

was  reached  the  silver  buttons  retained  copper  notwithstanding 
the  ratio  of  lead  to  copper  was  200  to  i.  As  the  per  cent  of 
copper  increased  the  tendency  of  the  silver  buttons  to  sprout 
increased,  which  no  doubt  is  due  to  copper  being  such  a  good 
absorbent  of  oxygen. 

The  Effect  of  Tellurium  on  the  Loss  of  Silver. — A  series  of 
tests  with  the  silver  constant,  lead  constant  (10  grammes),  and 
temperature  constant  at  775°,  but  the  tellurium  varying  from 
2.2%  to  15%,  showed  as  follows: 

The  loss  of  silver  seemed  to  remain  about  normal,  and  the 
buttons  appeared  bright  and  clear  until  15%  of  tellurium  was 
used,  when  the  resulting  silver  beads  had  a  dull  and  frosted  appear- 
ance on  the  surface.  These  buttons,  when  dissolved  in  strong 
H2SO4,  gave  the  characteristic  pink  color,  showing  the  presence 
of  tellurium. 

The  student  can  easily  see  from  the  foregoing  tables  how 
careful  he  should  be  in  the  cupelling  operation,  and  how  he  should 
endeavor  always  to  have  feather  litharge  crystals  upon  the  cupel. 

The  silver  losses  taking  place  in  both  scorification  and  cru- 
cible work  may  be  summed  up  as  follows : 

i  st.  Silver  carried  into  the  slag,  which  is  the  smallest  loss. 

2d.  Silver  volatilized  during  cupellation,  which  is  next  in 
amount. 

3d.  Silver  absorbed  by  the  cupel,  which  occasions  the  largest 
loss. 

In  the  ordinary  work  of  an  assay  laboratory  it  is  impossible  to 
assay  all  the  slags  and  cupels  so  as  to  determine  these  losses,  but 
they  can  be  determined,  and  in  the  assay  of  very  rich  material  and 
in  special  cases  the  corrections  are  made  as  in  the  Assay  of 
Zinc  Residues,  page  163. 

Parties  sending  samples  to  different  assayers  should  specify 
whether  they  wish  this  to  be  done  or  not,  for  I  have  known  samples 
to  vary  simply  because  one  assayer  was  making  the  corrections 
and  another  was  not. 

Silver  Beads  of  Unusual  Appearance. — Beads  containing 
certain  ratios  of  silver  and  gold,  when  cupelled  at  too  low  a  tem- 
perature near  the  blicking  point,  instead  of  continuing  to  drive. 


66  NOTES  ON  ASSAYING. 

flatten  out,  giving  a  gray,  mossy  bead.  This  is  due  to  the  presence 
of  some  8%  to  12%  of  lead.  Such  beads,  if  wrapped  in  lead  foil 
and  recupelled  at  a  higher  temperature,  will  blick  and  give  bright, 
rounded  buttons. 

Buttons  of  this  character  should  not  be  mistaken  for  those 
containing  a  large  amount  o)  platinum,  which  flatten  out  and 
have  an  appearance  somewhat  similar.  Repeated  cupellations 
will  not  alter  the  appearance  of  these  buttons. 

When  platinum  is  present  in  small  amount  the  silver  bead 
is  rough,  irregular,  and  a  high  temperature  is  required  to  blick  it. 
Tellurium  csuses  a  silver  or  gold  bead  to  appear  dull  and  frosted. 

ASSAY  OF    ORES   FOR  SILVER,   CRUCIBLE   METHOD. 

(POT-FURNACE;  COKE  FUEL.) 

The  object  here,  as  in  the  scorification  method,  is  to  form  a 
slag  from  the  gangue  or  waste  material  of  the  ore,  and  to  collect 
the  precious  metals  by  means  of  lead,  which  is  cupelled  afterwards. 

In  the  scorification  method  our  chief  fluxes  are  lead  and  borax 
glass,  with  an  addition  of  silica  in  some  cases  and  sometimes  a 
pinch  of  soda. 

The  free  access  of  air  gives  an  oxidizing  atmosphere.  In 
the  crucible  process,  on  the  other  hand,  although  we  make  U9e  of 
oxidizing  agents,  such  as  litharge  (PbO)  and  nitre  (KNO3),  we 
are  generally  using  reducing  agents,  and  the  crucible  being  covered 
up,  the  atmosphere  is  more  of  a  reducing  one. 

FLUXES   AND   REAGENTS. 

The  principal  fluxes  and  decomposing  agents  used  are  the 
following : 

Sodium  Carbonate  (melts  at  814°  C.)  and  Potassium  Carbon- 
ate (melts  at  885°  Le  Chatelier).  Both  are  most  important 
fluxes.  Either  bicarbonate  of  soda  or  sal-soda  may  be  used,, 
because  cooking-soda  is  decomposed  by  heat  as  follows: 

2NaHCO3+heat  =  Na2CO3  +  CO2-fH2O. 

Both  the  carbonates  act  as  basic  fluxes  and  combine  with  silica 
and  silicates  to  form  a  silicate  of  the  alkali  with  the  disengagement 
of  CO2 :         2Na2CO3  +  SiO2  =  2Na2O,SiO2  +  2CO2. 
This  gas  tends  to  make  them  oxidizing  agents. 


ASSAY  OF  ORES  FOR  SILVER.  67 

The  silicate  of  soda  formed  may  be  one  of  the  following, 
depending  upon  the  ratio  of  the  silica  to  the  carbonate  of  soda 
in  the  fusion: 


=  subsilicate. 
2Na2O,SiO2  =  monosilicate. 

=bisilicate,  i.e.,  62  to  60  or  about  neutral. 


=  sesquisilicate. 

The  following  charges,  fused  in  a  pot-furnace  in  an  E  crucible, 
will  illustrate  this: 

No.  i.         No.  2.       No.  3.       No.  4. 

Bicarbonate  of  soda,  grammes  ----     24         24        22         20 
SiO2,  "          ....     10         16        20        25 

No.  i  poured  clean  and  well,  and  the  resulting  product  was 
probably  the  sesquisilicate  of  soda.  Slag  very  stringy. 

No.  2  poured  out,  but  was  a  little  thick. 

No.  3  poured  part  way  out  of  the  crucible. 

No.  4  only  partly  fused. 

Both  carbonates  form  fusible  compounds  with  many  metallic 
oxides,  but  the  compounds  are  not  stable  and  are  readily  broken 
up  by  the  presence  of  carbon.  Carbonate  of  soda  I  consider 
one  of  the  most  important  if  not  the  most  important  flux  used 
in  assaying  sulphide  ores  by  the  crucible  method.  It  decomposes 
these  sulphides  and  in  the  case  ?f  galena  with  a  reduction  of  lead. 


If  Na2CO3  +  2C  are  heated  in  a  closed  vessel,  we  have 

2Na  +  3CO,     or     2Na2CO3-fC 
Also  Na2O  +  C  =  2Na  +  CO. 

Then 


The  amount  of  lead  thrown  down  seems  to  depend  upon 
the  amount  of  alkali  used,  as  shown  in  the  following  fusions. 

*  See  also  page  97. 


68  NOTES  ON  ASSAYING. 

Galena  (carrying  84$  lead),  grammes            15  15  15 

Bicarb,  of  soda,                                   "                   io  40  75 

Borax,                                                    ««                  IO  —  '          — 

Glass,                                                   »                    5  5  § 
Cover  of  salt  in  each  case. 

Time  of  fusion,  minutes 25  25  25 

Lead,  grammes None  .        9.15  9.89  or  78^ 

of  the  lead 
present 

Lead  matte,  grammes A  littlf  None  None 

Slag Thick,  did  not 

pour  well 
Slag,  color Black  Black          Black  and  gray 

The  carbonates  may  be  used  indifferently,  but  Na2CO3  is  to  be- 
preferred,  as  it  is  cheaper  and  does  not  deliquesce. 

Both  carbonates  together  make  a  more  fusible  mixture  than 
either  one  alone.  The  bicarbonate  NaHCOs  is  generally  used,, 
because  it  is  more  likely  to  be  free  from  sulphates. 

Borax,  or  biborate  of  soda  (Na2O,  2B2O3,  or  Na2B4O7-f- 
ioH2O),  melts  at  about  560°  C.  Soluble  in  water. 

This  is  an  excellent  and  universal  flux.  It  is  neither  oxidiz- 
ing nor  desulphurizing,  but  forms  fusible  compounds  with  all. 
the  bases,  and  fuses  and  combines  with  most  of  the  metallic  oxides. 
15  to  20  grammes  will  make  6  grammes  of  MgO  perfectly  liquid, 
while  60  grammes  of  PbO  will  not.  Owing  to  the  presence  of 
boracic  acid  it  acts  as  an  acid  flux,  but  is  not  as  strong  a  one  as, 
SiO2.  Too  much  in  a  fusion  has  the  same  effect  as  too  much 
SiO2,  rendering  the  fusion  thick.  Its  influence  on  the  size  of 
the  lead  button  may  be  to  increase  or  diminish  it,  depending 
upon  the  amount  used  and  the  character  of  the  ore.  It  may 
be  used  in  the  form  of  biborate  of  soda,  but  owing  to  the  large 
percentage  of  water  in  this  (47.2%),  which  causes  much  swelling 
in  the  crucible  or  scorifier,  it  is  better  in  all  scarification  work 
and  crucible  fusions  in  the  muffle  to  use  borax  glass. 

Borax  Glass. — This  is  ordinary  borax  fused  (loss  about  40 
per  cent),  poured  into  moulds,  and  later  on  broken  up  into  small 
pieces.  It  is  almost  twice  as  strong  as  common  borax,  and  costs 
25  cents  or  more  per  pound.  On  account  of  this  high  cost  it 
should  be  used  only  for  muffle-work  and  for  refining  bullion. 

Litharge    (sp.  gr.  9.2  to  9.36;     Pb  =  92.86%,  0  =  7.14%). — 


ASSAY  OF  ORES  FOR  SILVER. 


69 


Melts  at  about  950°  C.  Quick  cooling  is  said  to  promote  the 
yellow  color,  slow  cooling  the  red  color.  It  is  a  strong  oxidizing 
agent,  oxidizing  all  the  metals  except  Ag  and  Au;  also  all  the 
sulphides,  arsenio-sulphides,  etc.: 

Fe  +  PbO=FeO  +  Pb;         FeS2  +  5PbO 
Zn+PbO  =  ZnO+Pb;         ZnS  +  3PbO  =ZnO 


It  is  a  universal  flux,  forming  fusible  compounds  with  bases 
and  combining  with  SiO2  to  form  lead  silicates. 

The  silicate  formed  depends  upon  the  ratio  of  silica  and 
litharge  present  in  the  fusion,  and  this  fact  should  be  borne  in 
mind  when  silica  is  added  to  a  charge. 

The  silicate  formed  may  be  one  of  the  following: 

4PbO,SiO2  =  subsilicate. 

2PbO,SiO2  =  monosilicate  and  most  readily  fusible. 

2PbO,2SiO2  =  bisilicate. 

2PbO,3SiO2  =  trisilicate. 

These  are  all  fusible,  but  above  this  they  commence  to  become 
infusible,  and  when  we  have  2PbO,i8SiO2  the  mass  will  become 
only  pasty  even  at  a  very  high  temperature. 

Metallic  iron  will  decompose  these  silicates  either  partly  or 
wholly,  with  a  reduction  of  lead: 

2PbO,SiO2+  2Fe=  2FeO,SiO2+  2Pb. 

The  following  fusions  made  in  an  E  crucible  in  the  pot-fur- 
nace will  show  the  effect  of  SiO2  in  a  fusion  when  both  soda 
bicarbonate  and  litharge  are  present. 


No.  i. 

No.  2. 

No.  3. 

No.  4. 

No.  5. 

No.  6. 

Sodium  bicarbonate,  grammes  

1C, 

15 

1C 

15 

1C. 

1C 

Litharge,                                        
Argols                                  " 

60 
•2 

60 

•2 

60 

•2 

60 

•2 

60 
•2 

60 

-2 

SiO2                                     " 

24 

26 

•?o 

I? 

^6 

7Q 

Cover  of  salt  in  each  case. 
Ratio  of  SiO2  to  soda.  .  .           .    . 

Time  of  fusion,  minutes  

2C 

7=r 

25 

2C 

2C 

2C 

Lead,  grammes  

27 

26 

28 

24 

24 

No.  i.  S'ag  poured  well,  and  was  glassy.  No.  2.  Slag  poured  well,  was  glassy  and  green  in 
coli  r.  No.  3.  Slag  was  thick  and  contained  some  lead.  No-  4.  Slag  was  much  thicker  ;han  No.  3 
and  contained  more  lead.  No.  5.  Slag  was  lumpy.  No  6.  Slag  would  not  pour. 


70  NOTES   ON  ASSAYING. 

Although  litharge  is  a  strong  base,  it  forms  fusible  com- 
pounds with  oxides  infusible  by  themselves.  Fusible  mixtures 
are  thus  formed  with  lime  and  the  earths,  which,  though  bases 
themselves,  seem  to-  be  held  in  solution.  In  the  crucible  assay, 
although  acting  as  a  flux,  its  principal  use  is  to  supply  the  lead 
to  alloy  with  and  collect  the  silver  and  gold  in  the  ore.  When, 
brought  into  contact  with  carbon,  organic  matter,  metallic  sul- 
phides or  iron,  it  is  reduced  to  metallic  lead,  and  this,  while  settling 
in  a  spray  through  the  contents  of  the  crucible,  collects  all  the 
silver  and  gold  in  the  ore : 

2PbO+C       =  2Pb+CO2;* 
9PbO+ Sb2S3= 9Pb+  Sb203+  3S02; 
2PbO+PbS  =3Pb+SO2; 
PbO+Fe       =FeO+Pb. 

Iron. — This  is  a  desulphurizing  agent  and  separates  the  sul- 
phur from  Pb,  Ag,  Hg,  Bi,  Zn,  Sb,  Sn,  and  partly  from  Cu: 

PbS+Fe  =  FeS+Pb. 

It  also  decomposes  litharge  thus:  PbO  +  Fe  =  FeO+Pb;  owing  to 
which  reaction  some  assayers  use  it  to  throw  down  the  lead 
in  their  fusions,  but  I  wish  the  student  to  consider  it  as  a 
desulphurizer. 

It  decomposes  lead  silicate  as  follows: 

2PbO,SiO2+  2Fe  =  2FeO,SiO2+  2Pb. 

In  the  crucible  assay  it  is  used  either  in  the  form  of  nails 
and  spikes,  which  are  put  in  point  down,  or  as  iron  wire,  which 
can  be  twisted  into  any  desired  form. 

Iron  and  Arseniate  of  Soda. — From  the  following  fusions  it 
is  seen  that  arseniate  of  soda  when  present  in  a  fusion  with  litharge 
and  soda  does  not  reduce  lead  nor  form  a  speiss  with  iron  when 
the  latter  is  added. 


*  When  an  oxide  is  easily  reducible,  as  PbO,  the  gas  given  off  will  be  CO2. 
When  not  easily  reducible,  as  ZnO   then  CO  is  formed. 


ASSAY  OF  ORES  FOR  SILVER. 


Arseniate  of  soda,  grammes:  5 

Bicarb,  of  soda,  30 

Borax, 

Litharge,  30 

Silica, 

Iron  nails  (2o-penny).  .  . 


Time  of  fusion,  minutes.  .  . 

Lead,  grammes . 2< 

Speiss,       "       None 

Slag,  color White 


Cover  of  salt  in  each  case. 
3° 


9.6* 

5 

9.6* 

19.2 

3° 

3° 

3° 

30 

— 

— 

5 

5 

30 

30 

3° 

30 

— 

— 

3 

3 

— 

3 

3 

3 

Salt, 


3° 

None 
Drab 

30 
27.62 
None 
Black 

<~i 

3°  A 
23-65 
None 
Black 

3° 
16.4 
None 
Black  and 
thick;  lead 
globules 
present 

.  Yellow  with  Yellow  with      —    Grayish 
red  spots      red  spots 


*  Corresponding  to  3/io  A.T.  of  an  ore  containing  ao5/  0%  of  arsenic. 
f  The  small  amount  of  lead  thrown  down  in  the  first  two  fusions  is  no  doubt 
due  to  the  presence  of  some  arsenite  of  soda  in  the  arseniate. 

Iron  and  Arsenite  of  Soda.  —  The  following  fusions  show  that 
in  the  presence  of  litharge  an  arsenite  like  a  sulphide  throws 
down  lead  and  that  the  presence  of  iron  does  not  necessarily 
form  a  speiss. 


2.7 


Arsenite  of  soda,  grammes 

Bicarb,  of  soda,  "        

Borax,  "       ....... 

Litharge,  "        

Silica  (Si02),  "       

Iron  nails  (2o-penny) — 

Cover  of  salt  in  each  case. 


30 


5-4 


3° 


Time  of  fusion,  minutes  ...........  30 

Lead,  grammes  ..................  4.8 

Speiss,       "       ..................  None 

Slag,  color  .......................  Gray 


30 
8 

None 
Gray 


2.7' 

5 

3° 
3 


26.9 

0.42 

Black 


5-4 


30 

27.8 
None 
Black 


Salt,     "    Yellow  and  red 

*  Corresponding  to  3/10  A.T.  of  an  ore  containing  2O5/10%  of  arsenic. 


Charcoal;  Argols,  KHC4H4O6;  Cream  of  tartar,  C4H5KO6; 
Sugar, Ci2H22On;  Starch;  Flour  (Reducing  Power  (R. P.)  about 
15). — These  are  all  reducing  agents,  i.e.,  they  are  capable  of  re- 
moving oxygen  from  those  compounds  with  which  it  may  be  com- 
bined. They  are  used  in  the  crucible  assay  to  remove  oxygen  from 
the  PbO,  and  to  reduce  the  necessary  amount  of  lead  to  collect  all 
the  precious  metals  in  the  ore.  They  have  different  reducing 


72  NOTES  ON  ASSAYING. 

powers,  and  assayers  prefer  some  one  and  some  another.  Char- 
coal is  itself  infusible  and  does  not  combine  with  fluxes;  too 
much  will  therefore  render  an  assay  thick  and  infusible.  Flour 
is  always  easily  obtained,  so  it  is  most  commonly  used.  I  prefer 
crude  argols  or  cream  of  tartar,  because  on  heating  they  break 
up  into  carburetted  hydrogen,  carbon  monoxide,  K2CO3,  KHO, 
.and  finely  divided  carbon,  and  for  this  reason  act  both  as  a  flux 
.and  a  reducing  agent.  One  objection  raised  against  their  use 
is  that  they  cause  the  fusions  to  boil  excessively. 

Potassium  Nitrate  (melts  at  339°  C.)  and  Sodium  Nitrate 
(melts  at  316°  C.)  (both  neutral  to  litmus).  —  These  are  both 
powerful  oxidizing  agents.  They  fuse  without  alteration  at  a 
temperature  below  redness,  but  when  heated  more  strongly  they 
give  up  oxygen: 

2PbS+  2KNO3  =  2Pb+  K2SO4+  SO2+  2N; 
2Cu2S+  2KNO3  =  4Cu+  K2SO4+  SO2+  2N. 


(If  nitre  is  used  in  excess,  the  slag  will  contain  Cu2O  and  PbO.) 
In  the  above  way  the  nitrates  readily  decompose  the  sul- 

phides, arsenides,  etc.,  in  the  ore;  the  oxygen  set  free  readily  com- 

bines with  the  sulphur,  forming  SO2  and  the  sulphate  of  the  alkali 

used. 

They  do  not  oxidize  metallic  lead  very  rapidly  unless  it  is 

very  finely  divided  and  suspended  in  a  molten  mass,  as  shown 

in  the  following  tests: 

No.  i.  No.  2.  No.  3. 

•Granulated  lead,  grammes  .....  60  )     mixed       60  (bottom  of  crucible)        60 

Nitre  (KN03),  •«      ......  '5  \  crucible.     1  5  (on  top  of  lead)  15 

Salt  cover  salt  cover  salt  cover 

Resulting  lead  button  .........  42  44  42 

Fusion,  minutes  ..............  20  20  20 

For  the  determination  of  the  oxidizing  power  (O.P.),  seepage 
Si. 

Fe203  and  Mn02.  —  These  are  both  oxidizing  agents  and 
are  basic  in  action: 


ASSAY  OP  ORES    FOR  SILVER. 


73 


Bear  this  reaction  in  mind  when  assaying  an  ore  containing 
cither  of  these,  especially  in  the  case  of  roasted  concentrates 
which  previously  contained  iron  pyrites.  They  may  have  such  a 
strong  oxidizing  power  that  no  lead  button  will  be  found  from 
a  fusion  where  3  grammes  of  argols  (R.P.  10)  are  used. 


No.  i. 

No.  2. 

No.  3. 

20 

75 
7 

10 

55 

63 
iizing  p 

No.  4. 

Fe  O    grammes   

20 

60 
2 

9 
18 

20 

60 

2 
10 

9* 

18 
Oxi 

i  A.T.  of  roasted 
trates 
40  Na2CO3 
20  borax 
60  litharge 
4  argols  (R.P. 
10 

8 
40.8 

concen- 
=  10.2) 

or  i.i 

Litharge    "       

Areols        " 

<R.P.  =  9) 
Glass          "       

Cover  of  salt  in  each  case. 
"The     resulting     lead     button 
weighed  grammes            ... 

Jf  the  Fe2O3  had  not  been  present 
the  lead  button  should  have 

29.  16 

Silica  (SiO2). — This  is  a  strong  acid  flux.  It  is  used  when 
the  bases  in  an  ore  are  in  excess,  when  the  ore  is  deficient  in 
gangue  matter,  and  also  to  protect  the  scorifiers  and  crucibles 
from  the  action  of  litharge.  (See  under  Litharge,  page  69,  for 
the  silicates  formed.)  For  the  effect  of  too  much  SiO2  in  a 
fusion,  see  pages  69  and  96. 

Glass. — This  is  ordinary  window-glass  or  chemical  glass- 
ware ground  fine.  It  is  already  a  silicate  of  the  alkalies,  lime, 
lead,  or  all  of  these,  so  its  influence  upon  a  fusion  is  not  the  same 
or  as  marked  as  silica.  The  ingredients  of  the  glass  are  already 
wholly  or  partly  in  combination,  while  the  silica  is  free.  (See 
page  84.)  Its  use  in  crucible  work  is  recommended  for  those  com- 
mencing assaying,  for  it  seems  to  act  as  an  equalizer  in  the  chaige 
and  is  especially  advantageous  in  the  fusion  of  black  sands  from 
sluice-boxes  and  similar  material.  Such  products  generally 
contain  a  variety  of  minerals  mostly  acting  as  bases  and  it  is 
usually  necessary  to  add  both  borax  and  silica.  One  can  easily 
add  too  much  silica  and  have  trouble  in  the  fusion,  whereas 
a  little  too  much  glass  will  do  no  harm. 


74  NOTES  ON  ASSAYING. 

Fluorspar.  —  A  most  excellent  flux  for  baryta  or  heavy  spar. 

Salt.  —  This  is  used  as  a  cover  to  the  charge  to  keep  out  the 
air  and  to  clean  the  interior  surface  of  the  crucible,  preventing 
the  small  particles  of  lead  from  adhering  thereto.  It  smelts  at 
772°  C.  (Le  Chatelier). 

Some  assayers  object  to  the  use  of  salt,  claiming  that  it  is 
of  no  advantage  and  in  some  cases  causes  the  crucibles  to  crack.. 
This  has  not  been  my  experience,  however. 

CRUCIBLE    EXPERIMENTS    WHICH    MAY    CLEAR    UP    SOME    OF 
THE    FOREGOING. 

1.  14  grammes  PbO+3J  grammes  Fe  gave  12  grammes  of 
Pb  and  a  slag,  glassy  and  red  in  color. 

2.  14  grammes  PbO+3-5  grammes  Fe+-3  grammes  Char- 
coal.    Pb=  13  grammes,  i.e.,  all  the  Pb.     Slag  black  and  dull. 

3.  15  grammes  PbO  +  6.?  grammes  Tap  Cinder  (FeO)  +  £ 
grammes  Charcoal.     Pb  =  4  grammes.     Slag  black  and  infusible, 
lead  scattered  all  through  it.     (15  grammes  PbO  carrying  92.8% 
Pb  =  13.92  grammes  Pb.) 

4.  42  grammes  of  lead  placed  in  the  bottom  of  a  crucible, 
covered  with  slag,  fused  20  minutes,  and  poured  gave  42  grammes 
of  lead. 

5.  15    grammes  PbS  +  3^-   grammes   Fe    gave    lead  =  12  J 
grammes    (PbS+Fe  =  FeS+Pb),  also  an  iron  matte. 

6.  15  grammes  PbS+6.2  grammes  Tap  Cinder  -ff  grammes 
Charcoal.      Pb  =  9  grammes  (Fe+PbS  =  FeS+Pb)  and  an  iron 
matte.     The  slag  was  infusible,  probably  due  to  too   much  C. 


7.  15  grammes  PbS  +9  grammes  Fe  gave  Pb=i3  grammes  ; 
also  iron  matte. 

It  is  claimed  that  when  an  excess  of  iron  is  not  used  some. 
Pb  will  go  into  the  iron  matte.  No.  5  seems  to  confirm  this, 
although  the  amount  of  Pb  is  very  little  less  than  No.  7.  For 
if  56  parts  iron  will  reduce  207  Pb  (Fe+PbO  =  FeO  +  Pb),  one 
part  iron  will  reduce  3.69  Pb. 

In  15  grammes  PbO  there  are  13.92  grammes  Pb. 

.*.       '     =3.77  grammes  Fe  to  reduce  all  the  Pb  from  the  PbO. 


ASSAY  OF  ORES  FOR  SILYER.  75 

The  effect  of  fluxes  at  a  high  temperature  on  different  sub- 
stances. 

The  amount  of  each  flux  used  is  the  same  as  would  be  taken 
in  an  ordinary  assay. 

MgO. 

No.  of  fusion  ....................  i  2  3  4 

MgO  .....  .  .....................  6  grammes  taken  in  each  fusion  on  the  basis 

that  i  A.T.  of  ore  might  contain  20%. 
Bicarb,  of  soda,  grammes  .........          30 

Borax,  '  '        .........         —  20  15 

Litharge,  "        .........         —  60 

Silica,  "        .........  5 

No.  i.  Was  infusible. 

No.  2.  Was  the  most  liquid;    slag  was  glassy. 

No.  3.  Was  next  to  No.  2  in  fusibility,  slag  was  glassy. 

No.  4.  Was  a  little  lumpy;   slag  was  dull  in  appearance. 

Magnesia  being  a  base,  borax  and  silica  are  the  best  fluxesr 
for  they  act  as  acids.  Litharge  in  large  excess  can  be  used;. 
its  action  seems  to  be  that  of  dissolving  the  MgO  within  itself.. 

Clay. 

No.  of  fusion  ....................          5  6  7 

Clay  ............................  12  grammes  taken  in  each  fusion  on  the  basis 

that  i  A.T.  of  ore  might  carry  40%. 
Bicarb  of  soda,  grammes  .........          30 

Borax,  "        .........         —  20 

Litharge,  .........         —  60 

No.   5.  Was  very  thick  and  would  just  pour;    slag  pasty. 
No.  6.  Was  liquid,  but  very  stringy;   slag  was  glassy. 
No.  7.  Fused,  but  was  very  lumpy. 
Here  again  borax  seems  to  be  the  best  flux. 


(A  Lake  Superior  hematite  carrying  93.57%  Fe3O3  and  a  total  of  4.88%  of 
SiO2  and  AljO^  in  about  equal  amounts.) 
No.  of  fusion  .............  10         n         12         13         14  15         16         17 

Fe2Oa  (iron  ore)  ..........  12  grammes  were  taken  on  the     15         15       i  A.T. 

basis  that  i  A.T.  of  ore  might 
carry  40%. 

Bicarb,  of  soda,  grammes  24         36        —        —        40  40         30         60 

Borax,  —         —         20         —         20  —         20         20 

Litharge,  "          —        —        —         60         60  60         60         60 

Silica,  4  7         72 

Argols,  "_____  i  4  4  4 


76  NOTES  ON  ASSAYING. 

No.  10.  Was  a  long  time  fusing  and  would  only  just  pour 
after  a  very  high  temperature  of  an  hour. 

No.  ii.  Was  the  same  as  No.  10,  only  slightly  more 
liquid. 

No.  12.  Was  fused  in  about  20  minutes  and  poured  rather 
thick  at  the  end  of  half  an  hour. 

No.  13.  Was  fused  in  about  15  minutes,  except  a  slight 
scum  on  top.  Poured  well,  except  a  slight  scum,  at  the  end 
of  half  an  hour.  The  slag  from  this  and  No.  12  was  slightly 
magnetic. 

No.  14.  Gave  a  good  fusion  after  35  minutes.  Slag 
glassy. 

No.  15.  Poured  afer  35  minutes'  fusion,  but  was  rather  thick. 
Slag  was  dull  in  appearance  and  seemed  basic. 

No.  1  6.  Poured  well  after  35   minutes'  fusion. 

No.  17.  Poured  well  after  35  minutes'  fusion.  Crucible  only 
slightly  attacked. 

The  lead  buttons  from  Nos.  14,  15,'  16,  and  17  weighed 
between  30  and  35  grammes. 

Ferric  oxide  being  a  strong  base,  fusions  Nos.  15,  16,  and  17 
show  that  fluxes  acting  as  acids,  like  borax  and  silica,  are  absolutely 
essential.  Considerable  borax  should  be  used,  and  it  seems  safe, 
in  order  to  form  a  silicate  of  iron,  to  add  sufficient  SiO2  so  that 
the  amount  added  plus  what  is  judged  to  be  in  the  ore  shall 
be  30%  to  40%  of  the  ore  used.  Rathei  high  PbO  seems  advis- 
able, and  the  temperature  at  which  the  fusion  is  conducted  should 
be  very  high. 


No.  of  fusion  ........................      16         17         18         19  20  21 

Fe3O4  ...............................  12  grammes  were  taken  on  15  15 

the  basis  that  i  A.T.  of 
ore  might  carry  40%. 

Bicarb,  of  soda,  grammes  .............     24         36        —        —  30  30 

Borax,                         "       .............     —        —        20        —  15  — 

Litharge,                     "       .............     —        —         —         50  50  90 

Algols,                        "        .............     —  3  3 

Silica,                          "       .............     —        —        —        —  3  5 


ASSAY  OF  ORES  FOR  SILVER.  77 

Nos.  1 6  and  17  would  just  pour  after  25  minutes'  fusion; 
slag  magnetic. 

No.  1 8.  Poured,  but  was  thick;    slag  magnetic. 

No.  19.  Poured  at  the  end  of  10  minutes;  fusion  very  liquid, 
crucible  nearly  eaten  through.  Slag  magnetic. 

No.  20.  Very  liquid  after  30  minutes'  fusion,  but  slag  carried 
some  lead.  Crucible  eaten  into  a  good  deal.  In  this  fusion 
there  would  be  no  free  litharge  remaining  if  each  gramme  of 
argols  reduced  9  grammes  of  lead  and  each  gramme  of  silica 
Combined  with  7  grammes  of  litharge. 

No.  21.  A  good  liquid  fusion  yielding  a  30-gramme  lead 
button.  Slag  was  very  clean,  crucible  not  much  attacked.  There 
are  about  25  grammes  PbO  free  in  this  fusion. 

The  conclusions  to  be  drawn  from  these  fusions  seem  to  be 
as  follows: 

To  ensure  a  good  liquid  fusion  and  a  slag  free  from  lead, 
fluxes  acting  as  acids,  like  borax  and  silica,  must  be  used  to  com- 
bine with  the  iron  oxide,  which  is  a  base.  The  litharge  must 
be  high  and  in  excess  and  some  soda,  as  usual,  is  necessary. 
The  temperature  at  which  fusion  is  conducted  must  be  very 
high. 

Glass  may  be  used  in  place  of  silica. 

Mica  (Muscovite). 

No.  of  fusion 8  9  10 

Mica 6  grammes  taken  in  each  fusion  on 

the   basis   that    i   A.T.   of  ore 

might  carry  20%. 

Bicarb,  of  soda,  grammes 30 

Borax,  "       15 

Litharge,  "       60 

No.  8.  Was  very  thick  and  would  not  pour  from  the  cru- 
cible. 

No.  9.  Was  liquid  but  was  thicker  than  No.  10;   slag  glassy. 
No.  10.  Was  very  liquid,  slag  very  glassy. 
Litharge  is  evidently  the  best  flux  here. 


78  NOTES  ON  ASSAYING. 

Sulphates. — Action  in  presence  of  litharge. 
Zinc  Sulphate. — This  acts  neither  as  an  oxidizing  nor  reducing 
-agent. 

ZnSO4,                  grammes 10  10  10 

Bicarb,  of  soda,         "       None  10  10 

Litharge,                     "       80  80  80 

Glass,                         "       5  5  5 

Argols  (R.P.  9.6)       "       None  None  2 

Cover  of  salt  in  each  case. 

Time  of  fusion,  minutes 25  25  25 

Lead,  grammes None  None  19 . 25 

Slag,  color Spotted  Spotted  Yellow 

Salt,     "    Yellow 

Calcium  Sulphate. — This  acts  neither  as  an  oxidizing  nor 
reducing  agent. 

CaSO4,                  grammes 10  10  10 

Bicarb,  of  soda,         "       None  10  10 

Litharge,                     "       80  80  80 

Glass,                         "       5  5  5 

Argols  (R.P.  9.6)       "       None  None  2 

Cover  of  salt  in  each  case. 

Time,  minutes 25  25  25 

Lead,  grammes None  None  18.6 

Slag,  color Full  of  spots,  Clear  Yellow 

crust  in  cru- 
cible 

Lead  Sulphate. — No  reduction  of  lead  takes  place. 

PbSO4,  grammes 10 

Bicarb,  of  soda,         "       10 

Litharge,  "       80 

Glass,  "       5 

Cover  of  salt. 

Time,  minutes 25 

Lead None 

Slag,  color Yellow  gran- 
ular, crust 
in  crucible 

Sulphates. — Action  in  presence  of  litharge  and  sulphide  of 
lead. 

Calcium  Sulphate  acts  neither  as  an  oxidizing  nor  reducing 
agent  in  presence  of  either  or  both. 


4  ASSAY  OF  ORES  FOR  SILVER.  79 

Calcium  sulphate,  grammes 10  10 

Bicarb   of  soda,             "        10  10 

Borax,                             "        10  10 

Litharge  (928/10%  pb) "       None  80 

Galena  (84%  Pb),        "        15  15 

Glass,                             "       5  5 

Cover  of  salt  in  each  case. 

Time,  minutes 25  25 

Lead  and  lead  matte,  grammes..  .          10.6 

Lead,  "      ...         —  37-94* 

Slag,  color.  ..." —         Clear  and  black 

*  According  to  the  reaction  PbS+  2PbO  =  SO2+  3?b,  the  button  of  lead  should 
^veigh  38.5  grammes. 

Lead  Sulphate. — When  fused  with  lead  sulphide  a  reduction 
•of  lead  takes  place,  the  amount  brought  down  depending  upon 
the  amount  of  alkali  used. 

Fusion  No i             2             3  4            5  6 

Xead   sulphate   (if  pure,    68.3% 

Pb),               grammes 10           10           10  10           10  10 

Bicarb,  of  soda,          "        40           20           10  20           20  60 

•Galena  (84%  Pb),     "        None     None       15  15            15  15 

Glass,                         "       5            5            5  5            5  5 

Argols,                        "       .......    None         2         None  None         2  None 

Cover  of  salt  in  each  case. 

Matte,  grammes None     None     Large  .5         2.9  None 

Lead,           "       44       6.8     Small  14. 6f     lo.of  16.45 

bead 

Slag,  color *          Brown      —  —  Black 

*  Thick,  last  of  it  very  thick;   when  cold,  yellow  all  through   and  bluish  yellow 
on  top. 

.f  Lead  was  brittle,  caused,  no  doubt,  by  presence  of  sulphur,  which  was  also 
present  in  the  slag  in  considerable  amount. 

Fusion  No.  i  shows  that  a  slight  amount  of  lead  is  thrown 
down  by  the  bicarb,  of  soda  and  No.  2  shows  that  all  the  lead 
is  reduced  in  the  presence  of  a  reducing  agent  and  sodium  bicar- 
bonate. 

TESTING   REAGENTS. 

One  of  the  first  things  an  assayer  must  do  is  to  test  the  purity 
•of  his  reagents.  Lead  and  litharge  can  both  be  obtained  free 
from  silver  and  gold,  but  this  purity  is  only  brought  about  by 
special  refining.  As  gold  is  more  readily  removed  than  silver 
the  former  is  less  likely  to  be  present  than  the  latter.  Some 
lead  and  litharge  on  sale  carry  considerable  silver  and  sometimes 
gold;  therefore  we  find  it  absolutely  necessary  to  assay  every  new 
lot  received,  and  as  some  lots  run  very  unevenly,  they  require 
just  as  careful  sampling  as  any  ore. 


8o  NOTES  ON  ASSAYING. 

Granulated  Lead. — If  this  cannot  be  readily  purchased,  it 
can  be  made  by  melting  lead  at  as  low  a  temperature  as  possible, 
pouring  it  into  a  box  and  shaking  it  slowly,  in  a  horizontal  direc- 
tion, until  it  begins  to  congeal  or  become  pasty;  it  is  now  shaken 
very  rapidly  until  it  granulates.  Sift  through  a  i2-mesh  sieve 
and  remelt  what  does  not  pass  through.  The  loss  by  this  method 
will  not  be  over  one  per  cent.  It  can  also  be  made  by  blowing 
steam  through  a  stream  of  melted  lead. 

Testing  jor  Silver  and  Gold. — Assay  for  silver  and  gold  by 
scorifying  three  or  four  portions  of  120  to  160  grammes  each  in  3" 
or  4"  scorifiers.  If  necessary,  rescorify  the  resulting  buttons  and 
continue  to  do  this  until  the  buttons  are  srrull  enough  to  cupel.  If 
the  lead  runs  very  low  in  silver  and  gold,  twTo  or  more  buttons, 
may  be  combined  in  the  scorifier  or  cupel.  Weigh  the  bead  of 
precious  metals  and  part  for  gold.  Make  the  corrections  to 
apply  to  35,  45,  and  50  grammes  of  lead.  This  correction  has 
to  be  made  even  if  extremely  small,  for  otherwise  silver  and 
gold  might  be  reported  as  being  present  in  an  ore  when  it  was 
entirely  absent. 

Litharge. — Testing  for  Silver  and  Gold. 


Pot-furnace.    F,  G,  or  H  Crucible.  Muffle-furnace.     A  or  B  Crucible. 

4  A.T.  PbO  60  grammes  to  3  A.T.  PbO 

Mix       20  grammes  soda  10         "         soda 

10         "         borax  glass  8          "        borax  glass 


cru- 
cible. 


Mix 

in 

cru- 
cible. 


3!  argols*  3$  argols* 

4         "         silica  2          "         silica 

Cover  of  salt.  Cover  of  salt. 

*  Reducing  power  =  8. 

The  28  grammes  of  lead  thrown  down  by  the  argols  will 
collect  all  the  silver  and  gold  in  the  whole  amount  of  PbO  used* 
Weigh  the  bead  and  part  to  see  if  gold  is  present. 

In  assaying  some  samples  of  lead  and  litharge  it  is  necessary 
to  take  large  amounts  of  each,  because  they  carry  very  small 
amounts  of  the  precious  metals;  therefore  if  we  take  35  grammes 
of  lead  or  30  grammes  of  litharge,  we  may  not  obtain  a  bead  and 
yet  silver  or  gold  may  be  present.  For  this  reason,  especially  when 
assaying  ores  which  have  a  very  small  amount  of  silver  in  them, 
unless  C.P.  reagents  are  used,  I  prefer  lead  and  litharge  carry- 


ASSAY   OF  ORES  FOR  SILVER. 


8r 


ing  so  much  silver  that  a  bead  will  result  when  35  grammes 
are  used,  rather  than  lead  and  litharge  which  has  a  correction 
of,  say,  .0001 1  grammes  for  35  grammes,  figured  from  the  assay 
of  1 20  or  1 60  grammes.  A  correction  as  small  as  .00011,  to» 
be  accurate,  can  only  be  obtained  by  using  a  large  amount  of 
lead  or  litharge.  If  now  we  make  an  assay  of  an  ore  carrying 
a  very  small  amount  of  silver  and  use  only  35  grammes  of  lead 
or  litharge,  the  silver  bead  both  from  the  ore  and  the  lead  or 
litharge  will  very  likely  weigh  less  than  .000  n  grammes. 

Oxidizing  Power  (O.P.)  of  Nitre.— Nitre  melts  at  about  339° 
C.  Like  litharge  it  is  a  strong  oxidizing  agent  and  has  the  prop- 
erty of  oxidizing  sulphides  with  ihe  formation  of  SO2  and  sul- 
phate of  potassium. 

The  oxidizing  power  should  be  found  by  fusing  it  with  an  ore 
the  working  reducing  power  of  which  is  known. 

The  following  are  examples: 


FeS,  and 

Arsenopyrite. 

Concentrates. 

Chalcopyrite. 

Ore,                   grammes  . 

•••     3 

3 

3 

3 

2 

3 

Sodium  bicarb.       " 

...     6 

3 

6 

6 

2 

3 

Litharge,                 " 

...50 

60 

5° 

5° 

90 

9°- 

Nitre,                      "       . 

.  .  .   — 

4 

— 

4 

— 

4 

Silica,                       "       . 

...  — 

3 

— 

— 

I 

3 

Cover  of 

salt. 

Cover  of  salt. 

Cover 

of  salt. 

Time  of  fusion,  minutes. 

17 

19 

20 

15 

20 

20 

Lead,  grammes  

21    ^O 

A      71 

2<5  .  76 

8.34 

18 

92 

R  P. 

7    17 

H-  •  /  A 

8.58 

9 

•  T 

21.50 

4.71 

°-p 4.2  4.35  4.45 

The  average  value  of  this  lot  of  nitre,  after  many  fusions  with 
different  ores,  was  found  to  be  4.3,  and  this  value  was  confirmed 
by  the  size  of  the  lead  buttons,  when  the  regular  assays  of  the 
ores  were  made  and  a  large  amount  of  nitre  used. 

It  is  often  claimed  that  the  oxidizing  power  of  nitre  varies 
with  different  ores,  but  the  variation  is  no  more  than  shown  in 
the  previous  fusions,  provided  the  right  reducing  power  o]  the  ore 
is  used.  If  the  true  reducing  power  was  known  and  every  condi- 
tion kept  the  same  in  each  fusion,  the  oxidizing  power  would 
probably  be  found  to  vary  not  as  much  as  indicated. 


%2  NOTES  ON  ASSAYING. 

The  following  will  illustrate  how  easily  a  wrong  value  for 
nitre  may  be  obtained: 


No.  of  Fusion  .  . 

iss 

145 

146 

147 

117 

118 

156 

•Ore,         grammes.  .  . 

3 

3 

3 

3 

2 

3 

3 

NaHC03,      "       ... 

0 

3 

6 

9 

2 

6 

o 

Litharge,        " 

60 

60- 

60 

60 

80 

70 

60 

-Nitre,             "       ... 

•  — 

— 

— 

— 



4 

Salt 

cover  in 

each  case. 

Time,  minutes  

13 

10 

10 

IO 

jn 

xo 

*V 

I9 

*3 

Temp.,  deg.  C  

1240 

1320 

J33o 

1290 

1225 

II2O 

1265 

Lead,  grammes  

14.72 

18.93 

23.26 

23-32 

14.03 

23.02 

4-95 

R.P.  . 

4.OI 

6.?i 

7.7C 

1  .  11 

1  .  Cf> 

•7      fa 

The  R.P.  of  this  ore  is  7.7. 

If  the  oxidizing  power  of  nitre  is  based  on  fusion  155,  it  equals 

— —  or  2.44.     If  on  fusions  146  and  147  it  is  4.5.     If  on 

fusion  117  it  is  4.02. 

Either  of  the  values  4.5  or  4  is  close  enough  for  practical  work. 

To  figure  the  O.P.  from  the  regular  ore  fusions  is  not  safe, 
'unless  these  charges  are  made  up  on  exactly  the  same  basis  as  the 
preliminary  fusion  and  conducted  in  the  same  way,  for  the  size 
-of  the  resulting  lead  button  depends  upon  the  amount  of  soda, 
-borax,  litharge,  and  5VO2  added  to  the  charge,  the  amount  of  gangue 
in  the  ore,  and  the  temperature  at  which  the  fusions  are  conducted. 

The  oxidizing  power  does  seem  to  vary,  based  on  the  lead  but- 
tons, with  different  reducing  substances  like  argols,  charcoal, 
flour,  etc.,  as  shown  in  the  following  fusions.  When  the  nitre  is 
kept  constant  and  the  litharge  varies,  as  in  fusions  Nos.  55  and  47, 
the  oxidizing  power  varies,  which  seems  to  indicate  that  the  varia- 
tion is  due  to  the  fluxes,  temperature,  or  something  other  than 
the  nitre.  Therefore  do  not  use  the  oxidizing  'Value  found  in  this 
manner,  when  making  up  a  charge  for  an  ore. 


No.  55-      No.  47 

Argols,  grammes.  .  . 

333  Charcoal  i         i      Starch  2^ 

2*                2i 

Soda, 

333 

3         3 

3 

3            3 

Litharge,    " 

60         60       100 

60       60 

60       100           60 

~Nitre, 

4           4 

—        4 

— 

4            4 

•SiO* 

333 

3        3 

3 

3            3 

Cover  of  salt. 

Cover  of  salt. 

Cover 

of  salt. 

Temp.,  deg.  C  

1060     1225     1090 

1160     1210 

1150 

1160      1220 

Lead,  grammes.  .  .  . 

29.78*  12.47  12.55 

27-57     8-42 

30.38! 

10.54     9.64 

O.P.  of  nitre  

4-33     4-3° 

4.8 

4.96     5.18 

*  Average  of  four  fusions.  t  Average  of  two  fusions. 


ASSAY  OF  ORES  FOR  SILVER.  83 

Reducing  Agents  (Charcoal  and  Argols). — Testing  for  Reduc- 
ing Power  (R.P.). — Before  the  student  attempts  to  assay  an  ore 
by  the  crucible  method  he  should  determine  the  reducing  power  * 
of  his  reducing  agents,  as  charcoal,  argols,  and  flour.  The  object 
of  this  is  twofold: 

i  st.  To  obtain  their  values  in  order  to  know  what  amount  of 
them  to  use  in  the  regular  fusion  of  the  ores. 

2d.  To  learn  the  principal  steps  connected  with  a  fusion  in  a 
crucible.  Take  two  crucibles,  either  E  or  F. 

Into  them,  in  the  order  given,  weigh  out  carefully  the  following: 


Litharge 60      grammes 

Bicarb,  soda.  .  3 

Argols 3 

Silica  (SiO2).  .  2 


or 


.  Glass 5-10 


Litharge 60  grammes  • 

Bicarb,  soda.         3 
Charcoal.  .    .        i 

Silica 2 

or 
Glass 5-10 


1 


Weigh  out  the  argols  and  the  charcoal  on  the  pulp-balance,  the  others  on  the 
flux-balance. 

Cover  of  salt,  \"  deep.  Cover  of  salt,  \"  deep. 

The  mixing  in  the  crucible  is  done  by  holding  the  crucible 
slightly  inclined,  and  while  revolving  it  in  one  hand,  with  the 
iron  spatula  continually  bring  the  material  up  from  the  bottom 
of  the  crucible.  When  finished,  hit  the  crucible  sharply  all 
round  to  settle  the  contents  and  remove  any  material  clinging 
to  the  inside  above  the  charge  and  then  put  on  the  cover  of  salt. 

The  cover  of  salt,  when  melted,  keeps  out  the  air,  washes 
down  and  cleans  the  sides  of  the  crucible  and  makes  a  glaze,  thus 
preventing  the  lead  globules  from  sticking  to  the  sides  of  the  cru- 
cible. Have  a  good  bright  fire,  then  sprinkle  over  it  a  thin  layer 
of  fresh  coke,  to  prevent  the  crucibles  coming  directly  in  con- 
tact with  the  hot  coals,  and  next  place  the  crucibles  in  the  furnace ; 
put  a  cover  on  each  crucible  to  keep  out  all  dust  and  coke;  care- 
fully pack  coke  around  them,  and  do  not  disturb  in  any  way 
until  the  contents  fuse.  The  top  of  the  crucibles  should  be  below 
or  only  slightly  above  the  bottom  of  the  flue.  Urge  the  fire  and 

*  When  we  speak  of  the  reducing  power  here,  we  mean  the  amount  of  lead 
that  i  gramme  of  the  substance  will  reduce  or  throw  down  from  an  excess  of 
litharge. 


84 


NOTES   ON  ASSAYING. 


heat  the  crucibles  until  the  contents  begin  to  fuse,  then  check  the 
fire  and  see  that  the  contents  of  the  crucibles  do  not  boil  over.  When 
the  contents  are  fairly  quiet,  put  the  draft  upon  the  fire  and  heat 
at  a  high  temperature  (noo  C.  or  over)  for  15  to  20  minutes 
or  until  the  fusion  is  perfectly  quiet.  The  reaction  which  has 
been  going  on  is  2PbO  +  C  =  2Pb  +  CO2,  which  will  continue  until 
all  the  carbon  present  has  been  oxidized  by  the  oxygen  in  the-  PbO 
present.  Take  the  crucible  out  of  the  fire,  and  pour  the  fusion 
into  a  mould  which  has  been  coated  with  chalk,  ruddle  (Fe2O3),  or 
oil,  previously  heated  and  dried.  When  cold,  separate  the  lead 
from  the  slag,  hammer  into  a  cube,  and  weigh  to  the  first  place  of 
decimals  on  the  pulp-balance.  Suppose  they  weigh  29  and  24 
grammes  respectively;  it  means  that  the  reducing  power  of  i 
gramme  of  charcoal  is  29  grammes  of  lead,  and  of  argols  8  grammes 
of  lead  (?34),  and  that  they  will  reduce  this  amount  of  lead  from 
an  excess  of  PbO,  whether  the  amount  of  PbO  is  60  or  1000 
grammes.  The  excess  of  litharge  remains  as  litharge  or  com- 
bines with  a  portion  of  the  crucible  and  forms  a  lead  silicate. 
If  we  use  only  20  grammes  of  litharge,  some  of  our  reducing 
substance  would  be  left  unoxidized  and  our  reducing  power 
would  be  too  low  and  therefore  inaccurate.  Both  fusions  can 
be  made  without  the  silica  (SiC>2)  or  the  glass,  which  are  added  to 
form  a  slag  with  the  excess  of  litharge  present  and  to  prevent  the 
PbO  from  combining  with  the  constituents  of  the  crucible  and 
eating  through.  The  glass  has  less  effect  than  silica,  because  it  is 
already  a  silicate  of  lime,  soda,  potash,  lead,  or  a  mixture  of 
these,  and  is  preferable  for  those  commencing  assaying.  The 
silica  is  SiO2  and  has  a  great  influence  upon  the  results,  as  the 
following  fusions,  made  in  a  pot-furnace,  will  show. 


Bicarb,  soda,  gins.. 

3 

6 

12 

3 

Litharge  

60 

60 

60 

60 

60 

60 

60 

60 

60 

fin 

Argols 

•2 

2 

a 

3 

3 

3 

3 

Glass 

_  _  _ 

IO 

20 

•     --- 

Silica  (SiO2)    ... 

f 

Cover    of    salt    in 

0 

3 

each  case. 

["  Temp,  outside  of 

crucible,  deg.  C. 
1  Lead  button,  gm. 
[  Reducing  power. 

1220 
29.03 
9.68 

940 
28.9 

9-63 

1250 
27.7 
9.24 

940 
28.7 
9-55 

940 

28.03 
9-34 

940 
24.81 

8.27 

1280 
29.69 
9.90 

*345 
30-83 
10.28 

1320 

30-75 
10.25 

1060 
29.28 
9.76 

Time  of  fusion  between  1 2  and  20  minutes. 


ASSAY  OF  ORES  FOR  SILVER.  85 

In  other  words,  when  60  grammes  of  PbO  and  3  grammes  of 
argols  are  used,  the  addition  of  soda,  up  to  6  grammes,  increases 
the  size  of  the  lead  button;  beyond  this  it  has  little  if  any  effect. 
The  limit  for  the  silica  is  evidently  between  2  and  3  grammes, 
for  3  grammes  diminish  the  size  of  the  lead  button,  and  5  grammes 
have  a  marked  effect.  If  the  lead  silicate  2  PbO,SiO2  is  formed 
(a  ratio  of  7  PbO  to  i  SiO2),  then  no  excess  of  PbO  would  be  left 
in  the  fusion  when  5  grammes  of  SiO2  were  used,  and  carbon 
cannot  reduce  lead  from  a  lead  silicate. 

The  SiO2  used  contained  98.68%  SiO2.  The  glass  seems  to 
have  about  one  fifth  the  effect  of  the  silica,  i.e.,  i  SiO2  =  5  glass. 

The  results,  when  using  charcoal,  were  as  follows: 


Bicarbonate  of  soda,  grammes  
Litharge,                          "       

60 

60 

60 

Charcoal,                           "        
Glass,                                "        

i 

I 

I 

IO 

Silica,                                 "        

T. 

•i 

Cover  of  salt  in  each  case. 
C  Time   minutes 

It 

It; 

I  "t 

Temperature   degrees  C.  . 

122^ 

1  300 

T»*7 

|  Lead    grammes 

*"3 

27.8i; 

*j*~ 

27    38 

27    57 

1  Reducing  power.  .       

27    8« 

*/    o" 

27.  28 

27    57 

The  effect  of  too  much  silica  or  glass  will  be  shown  when  the 
value  of  any  other  reducing  agent  is  obtained  in  the  same  way 
by  substituting  it  in  place  of  argols  or  charcoal  and  keeping  the 
rest  of  the  charge  the  same. 

The  reasons  for  not  making  these  fusions  with  litharge  alone 
and  the  reducing  agent  are  twofold:  first,  because  by  using 
the  silica  and  soda  we  approximate  somewhat  to  the  charge  for 
the  regular  fusion;  and  second,  because  a  crust  is  prevented. 
A  fusion  may  be  at  a  very  high  temperature  and  liquid  below, 
but  a  crust  on  top  will  prevent  a  clean  pour.  Small  amounts  of 
silica,  soda,  or  borax  prevent  this,  and  the  whole  charge  will  be 
liquid.  If,  when  these  fluxes  are  present,  a  crust  forms  or  the 
fusion  is  thick,  it  is  due  to  either  too  low  a  temperature  or  an 
*  excess  of  some  flux. 

The  effect  of  borax  and  borax  glass  is  similar  to  that  of  silica, 
although  not  so  marked : 


86 


NOTES  ON  ASSAYING. 


Litharge,  grammes. 
Argols,  "        . 

Borax-glass,     " 
Borax,  " 


Time  of  fusion,  minutes. 

Temp,  outside  crucible,  deg.  C. 

Lead,  grammes 

Reducing  power 


60 
3 


12 

I22O 
29.03 

Q.68 


60 
3 
3 


Cover  of 

13 
860 
28. 
9.46 


3928 


6o 
3 
5 

salt 


860 

49 
9-5° 


60 

3 
10 


in 
16 

860 
27.22 

9.07 


60 
3 

3 

each 
10 

1240 
28.77 
9-59 


60 
3 

6 

case. 

ii 

860 

7-5i 
9.17 


60 
3 


60 
3 


10 

1225    1330 
26.7825.99. 
8.92    8.66 


From  this  table  6  grammes  of  borax  have  about  the  same 
effect  as  10  grammes  of  borax  glass. 

Incorrect  results  may  also  be  obtained  by  not  having  the  heat 
high  enough,  as  shown  in  the  following: 


Pot-furnace.     B  Crucible. 


Muffle.     B  Crucible. 


B  «      Bicarb,  soda.  . . .     3  gm.  3 

•~  3  I  Litharge 60  c '  60 

g  g  I  Argols 3  ' '  Charcoal     i 

u   [  Glass 10  "  Glass         10 

Cover  of  salt  Cover  of  salt 

Lead 31.1  "  27.5 

Reducing  power  10.36  27.5 


3 
60 
Argols      3 
Glass     10 
Cover  of  salt 
28.1 
9.4 

3 
60 
Charcoal     I 
Glass         10 
Cover  of  salt 
26.4- 
•6*4, 

ASSAY  OF  ORES    FOR   SILVER:    CRUCIBLE    METHOD. 

Having  tested  the  reducing  agents  and  found  their  values,  to- 
be  used  in  all  subsequent  work,  we  can  now  take  up  the  assay  of 
an  ore.  The  principal  advantage  of  the  "crucible  method/' 
whether  for  assaying  ores  for  silver  or  for  gold,  is  that  we  can  use 
large  amounts  of  ore.  It  is  therefore  especially  adapted  to 

(a)  Poor  or  low-grade  ores,  i.e.,  ores  poor  in  silver  and  gold. 

(b)  Refractory  ores,  or  those  with  a  refractory  gangue  like 
limestone,    barite,  etc.,  which   require   large  amounts   of   borax 
glass  or  some  other  flux  to  decompose  them  in  the  scorifier. 

(c)  Special  ores  like  chloride  of  silver,  which  spit  badly  in 
the  scorifier. 

Avoid  if  possible  using  the  method  jor  ores  containing  large 
amounts  of  copper,  antimony,  and  like  metals,  which  are  liable  to- 
be  reduced  and  pass  into  the  lead  button,  and  hence  to  necessitate 
a  scorification.  (See  special  methods,  pp.  118  and  122.) 

We  may  divide  the  ores  for  crucible  work  into : 


ASSAY  OF  ORES  FOR  SILVER.  87- 

Class  I.  Silicious,  oxide,  and  carbonate  ores  or  ores  con- 
taining no  sulphides,  arsenides,  etc.,  i.e.,  ores  with  no  reducing 
power,  or  which  are  unable  to  decompose  litharge  with  a  reduc- 
tion of  lead. 

Class  II.  Ores  carrying  sulphides,  arsenides,  or  organic 
matter,  i.e.,  ores  having  a  reducing  power  or  ores  which  can, 
decompose  litharge  with  a  reduction  of  lead. 

The  character  of  the  sample  of  ore  can  of  course  be  most, 
readily  determined  when  the  ore  is  in  a  coarse  condition  or  in 
lumps,  but  as  fully  half  the  samples  received  by  the  assayer  are 
in  a  pulverized  condition,  he  must  be  able  to  form  a  very  closer 
idea  of  their  composition. 

Given  a  sample  of  pulverized  ore  to  assay  either  for  silver  or 
gold,  or  for  both,  the  student  should  ask  himself  the  following: 
questions : 

(a)  Is  the  ore  sufficiently  fine  to  assay,  i.e.,  will  it  pass  through 
a  loo-mesh  sieve  or  a  finer  one? 

(b)  What  is  the  character  of  the  sample,  i.e.,  what  minerals 
are  present?    Are  they  sulphides,  oxides,   carbonates,  or  other 
compounds  ? 

(c)  Is  the  sample  apparently  an  iron,  copper,  lead,  or  zinc 
ore,  or  is  it  a  mixture  of  several  minerals  ? 

(d)  Is  there  much  gangue  and  is  this  gangue  acid  or  basic,, 
i.e.,  is  the  gangue  quartz  and  silicious,  or  does  it  consist  of  basic- 
material,  such  as  iron  oxide  or  limestone? 

(e)  Is  the  sample  better  adapted  for  the  scorification  or  for 
the  crucible  method  ? 

All  these  questions  have  a  bearing  upon  the  actual  assay;, 
for,  as  in  chemistry  we  use  certain  methods  in  the  separation  of 
certain  elements,  so  in  assaying  certain  methods  must  be  used 
upon  certain  classes  of  ore. 

The  fluxes,  reagents,  sizes  of  scorifier,  crucibles,  and  heat 
used  depend  upon  the  nature  and  composition  of  the  sample. 

Given  an  ore,  let  the  student  empty  the  whole  of  it  out  of  its 
receptacle  and  mix  or  roll  it  100  times  on  oilcloth  or  glazed 
paper.  Now  take  a  very  small  portion  of  it,  place  it  in  a  horn 
spoon,  a  dish,  vanning-shovel,  or  gold-pan,  moisten  it  with  water 
and  shake  it  gently;  this  will  cause  any  heavy  material  that  may 


88  NOTES  ON  ASSAYING. 

be  present  to  settle  out.  By  gently  washing  off  the  lighter  portion 
the  student  can  examine  the  heavy  portion  or  concentrates,  if  any 
are  present,  and  decide  whether  it  belongs  to  Class  I  or  Class  II. 

Having  decided  whether  the  ore  contains  sulphides  or  not, 
proceed  to  weigh  out  the  fluxes  on  a  flux  balance  and  place  them 
in  the  crucible.  The  ore  is  weighed  out  last  of  all  on  a  pulp-balance, 
and  brushed  from  the  scale-pan  into  the  crucible,  where  it  should 
be  thoroughly  mixed  with  the  fluxes. 

If  the  ore  is  weighed  out  first  it  is  apt  to  be  left  at  the  bottom, 
where  it  will  merely  sinter,  stick  to  the  crucible,  and  never  be 
decomposed. 

Some  prefer  to  mix  the  ore  and  fluxes  on  paper  and  then 
transfer  the  mixture  to  the  crucible,  but  this  seems  to  me  unneces- 
sary, for  a  thorough  mixing  can  be  done  in  the  crucible,  thereby 
avoiding  losses  on  paper  and  in  transferring. 

The  amount  of  ore  taken  can  be  any  weight  from  ^  A.T. 
to  4  A.T.,  but  the  fluxes  must  be  in  proportion.  The  crucible 
should  never  be  more  than  two  thirds  full  when  the  charge  is  all 
in  and  the  cover  of  salt  placed  on  top. 

Class  I.  Ores  under  this  class  are  assayed  upon  the  following 
plan.  (Pot-furnace,  E  or  F  crucible.) 

SILICIOUS  ORE. 

Charge  (a).                                                           Charge 
Jtjt  [Ore |  A.T.  Ore 

"£3   I  Bicarb,  soda,  grammes..     30  Bicarb,  soda,  grammes.. 

"•-  %  \  Borax,  "  0-3  Borax,  " 

a  o      Litharge,*  "  30  Litharge,* 

•^       lArgols,t  3i  Argols,f 

Cover  of  salt  J  inch  thick  over  all. 

*  Sufficient  £>  supply  25  to  28  grammes  of  lead. 

f  Each  gramme  reduces  8  grammes  of  lead. 

Each  fusion  should  give  a  lead  button  weighing  26  grammes. 

The  fluxes  are  always  weighed  out  first  and  placed  in  the  cruci- 
ble, and  the  ore  last  oj  all.  Mix  thoroughly  in  the  crucible,  strike  the 
crucible  several  times  on  the  outside,  and  then  place  the  cover  of 
salt  on  top,  which  washes  down  the  interior  of  the  crucible  and 
prevents  excessive  boiling  of  the  contents. 

For  the  reducing  power  of  argols,  take  the  value  you  find  when 
Jesting  reagents,  page  83.  Other  reducing  agents,  like  charcoal, 
flour,  starch,  etc.,  can  be  used,  but  their  reducing  power  must 
l)e  known. 


ASSAY  OF  ORES  FOR  SILVER.  89 

As  ores  are  often  assayed  in  duplicate,  the  student  is  recom- 
mended to  vary  the  charge  used  and  therefore  to  make  one 
fusion  as  per  charge  (a)  and  the  other  as  per  charge  (b).  A 
good  plan  to  follow  is  to  have  the  amount  of  active  fluxes  two 
or  more  times  greater  than  that  of  the  ore  used.  For  instance,. 
in  charge  (a)  the  soda  is  high  and  the  litharge  is  low.  The 
latter  disappears  to  give  the  lead  button,  and  the  argols  disappear, 
with  the  exception  of  a  little  KOH  and  K2CO3,  which  we  may 
neglect.  Therefore  the  active  fluxes  remaining  are  30  grammes 
of  soda  and  5  grammes  of  borax,  or  35  grammes  in  all,  i.e.,  a 
little  more  than  twice  the  ore  used  (J  A.T.).  If  we  put  the 
.soda  down  to  15  grammes,  then  we  should  have  only  20  grammes 
of  active  fluxes,  and  with  many  ores  this  would  be  insufficient  to 
insure  a  good  liquid  fusion. 

In  charge  (b)  the  soda  is  low  and  the  litharge  is  high,  so  our 
active  fluxes  are  15  grammes  of  soda,  5  grammes  of  borax,  and 
30  grammes  PbO,  or  50  in  all,  which  is  3^  the  amount  of  ore,  and 
the  fusion  will  probably  be  more  liquid  than  charge  (a). 

Although  the  two  charges  given  may  work  well  on  a  silicious 
ore,  it  must  be  borne  in  mind  that  the  fluxes  have  to  be  varied 
•according  to  the  gangue  of  the  ore  and  the  minerals  contained 
therein.  If  the  ore  carries  much  lime  or  is  high  in  metallic  ox- 
Ides,  the  borax  should  be  increased  or  SiO2  added.  If  barite  is 
present,  fluor-spar,  borax  or  silica  must  be  added  as  a  flux.  If 
Fe2Os  or  MnO2  is  present  in  large  amount,  the  reducing  agent 
must  be  increased  if  we  do  not  know  the  oxidizing  power  of  the 
ore,  because  they  will  be  reduced  to  the  lower  oxides  (FeO  and 
MnO)  by  the  argols,  and  not  enough  argols  will  be  left  to  reduce 
the  necessary  24  or  28  grammes  of  lead.  (See  pages  72  and  73.) 

The  following  charges  may  make  the  matter  a  little  clearer. 

Use  E  or  F  crucibles. 
Charge  (c)  (d)      _  (<*')  (*) 

--  '  ----  N       Gangue  =» 

Limestone  in  the  gangue.  oJ^t^-*.  ^nl^n^ 

magnesia. 


("Ore  ..........  $  A.T.  Ore  ..........   £  A.T.  *  A.T. 

Jtj  0      Bicarb,  soda  .  .  .gms.  15  Bicarb,  soda.,  .gms.  15  30  30 

a  §  j  Borax  ........    "     10  Borax  .........   '  '     10  10  10 

~£  g  1  Litharge  ......     "    60  Litharge  ......    "     60  30  40 

S  °     Argols  (R.P.-8)  "      3i  Argols  .......    "       4  6  3 

I  Silica  (SiO2)  .  .  .    "      2  Silica  .........    "       o  2  $ 

Cover  of  salt  in  each  case. 


po  NOTES  ON  ASSAYING. 

Charge  (c). — The  ore  is  basic,  therefore  borax  and  silica, 
both  acid  fluxes,  are  used;  the  litharge  is  also  kept  high,  for, 
though  acting  as  a  base,  it  is  a  good  flux  for  limestone. ' 

Charge  (d). — The  ore  is  partly  basic  due  to  the  Fe2O3,  for 
which  reason  borax  is  used,  and  partly  acid,  due  to  the  SiO2> 
for  which  reason  the  PbO  is  kept  high.  The  ore  also  has  an 
oxidizing  power  which  would  consume  i  gramme  of  argols  in 
reducing  the  Fe2O3  to  FeO,  hence  the  argols  are  raised  to  4. 

Charge  (df). — In  this  charge  the  argols  are  used  in  excess, 
therefore  the  amount  of  PbO  must  be  limited  to  30  grammes. 
An  excess  of  argols  does  no  harm,  and  this  is  an  instance  of  their 
advantage  over  charcoal;  for  if  the  latter  was  used  in  large  excess, 
the  charge  would  be  infusible.  Owing  to  the  PbO  being  low, 
the  soda  and  borax  are  high,  and  SiO2  is  added,  which  also  makes 
correct  the  ratio  of  fluxes  to  ore.  This  charge  would  not  be 
suitable  for  an  ore  carrying  copper  or  a  metal  that  could  be 
reduced,  for  the  reducing  agent  is  in  excess. 

Charge  (e). — The  ore  here  is  a  very  refractory  one  which  re- 
quires high  borax  and  considerable  silica. 

Fusion  in  Pot-furnace — General  Directions. — Fresh  fuel  is 
put  on  the  fire  and  the  crucibles  are  placed  on  this  (furnace 
will  hold  four).  Covers  are  put  on  the  crucibles  and  the  fuel 
is  packed  around  them  even  with  the  top  of  the  crucible,  then 
the  draft  is  put  on  the  furnace  and  the  contents  of  the  crucibles 
melted  slowly  to  avoid  dusting.  When  the  contents  first  fuse, 
lessen  the  draft  and  have  the  fusion  take  place  quietly,  not  only 
to  avoid  having  the  contents  boil  over,  but  also  to  prevent  the 
fusion  from  coming  up  on  the  sides  and  leaving  particles  of  ore 
and  lead.  When  all  danger  of  boiling  over  has  ceased,  seize 
the  crucibles  with  the  tongs  and  rotate  the  charge  several  times 
while  the  crucible  is  in  the  furnace,  then  increase  the  heat  and 
fuse  until  quiet,  say  30  to  45  minutes.  Rotate  the  crucible  several 
times  during  the  fusion.  As  a  rule,  the  larger  the  amount  of  sul- 
phides present  the  longer  the  fusion  will  have  to  be  in  order  to  insure 
perfect  decomposition  of  the  ore.  Magnetites  and  other  refrac- 
tory ores  require  a  long  fusion  and  a  high  temperature.  If  nails 
are  used  (ores  of  Class  II),  the  crucible  should  be  left  in  the  fire 
until  no  drops  of  lead  are  seen  adhering  to  the  nails,  when  they 


oo 

00 


ASSAY  OF  ORES  FOR  SILVER.  91 

are  raised  out  of  the  fusion.  When  the  fusion  is  completed, 
remove  them  and,  holding  them  partly  in  the  fusion,  tap  them 
gently  to  knock  off  any  adhering  drops  of  metal.  Let  the  cru- 
cible stay  in  the  furnace  two  or  three  minutes  longer,  then 
take' it  out  with  the  crucible- tongs,  tap  it  gently 
upon  the  furnace,  and  pour  the  contents  into  a 
mould,  which  should  have  been  previously  coated 
with  ruddle,  chalk,  or  oil  and  then  warmed. 
Allow  plenty  of  time  for  the  assay  to  cool,  and 
then  separate  the  slag  from  the  button  of  lead, 
which  should  be  soft  and  malleable.  If  thick  cast-iron  moulds 
are  used  the  assay  cools  almost  immediately.  Hammer  the 
button  into  a  cube.  Notice  the  button  carefully,  also  the  slag 
and  the  crucible,  for  by  so  doing  mistakes  in  the  subsequent  work 
may  be  avoided.  Weigh  the  button  on  the  flux-balances  to  the 
nearest  gramme.  If  the  button  is  hard  and  brittle,  it  should  be 
scorified  before  cupelling.  A  red  slag  indicates  copper  oxide 
(Cu2O) ;  if  the  salt  cover  is  blue,  it  also  indicates  copper,  due  to 
CuSO4  or  chloride  formed  with  the  salt.  The  button  should 
stick  slightly  to  the  slag.  A  button  falling  away  from  the  slag 
indicates  too  great  a  heat  or  too  long  a  fusion.  If  there  is  a  matte 
between  the  button  and  the  slag  it  indicates  too  short  a  fusion  or 
imperfect  decomposition.  Hard  buttons  are  due  to  the  presence 
of  copper  or  antimony  or  both. 

Brittle  buttons  may  contain  Cu,  Sb,  As,  Zn,  S,  PbO,  or  it  may  be 
a  rich  alloy  of  Pb  and  Ag  or  Pb  and  Au.  (14  grammes  Au,  27  Pb> 
brittle.)  23.5  grammes  Pb,  3.2  grammes  Au,  .3  gramme  Ag,  alsa 
brittle.  The  lead  button,  containing  the  precious  metals,  is  cu 
pelled  if  it  weighs  30  grammes  or  less.  If  it  weighs  over  this  or  con- 
tains impurities,  it  should  be  scorified  and  then  cupelled.  Cupel 
in  the  usual  manner.  The  silver  button  is  weighed,  correction 
made  for  the  Ag  contained  in  the  PbO  used,  and  the  result  reported 
in  ounces  per  ton,  and  value  per  ton  of  2000  Ibs.  av.  In  all 
crucible  assays  the  object  is  to  form  a  liquid  slag  by  means  of  the 
soda,  borax,  PbO,  and  other  fluxes.  The  litharge  is  a  splendid 
flux,  but  its  main  duty  is  to  supply  the  lead  and  to  collect  the 
precious  metals  in  the  fusion.  This  Pb  (brought  down  by  the 
argols,  sulph'des  in  the  ore,  or  iron  used  in  the  fus'on)  settles  as  a 
fine  spray  through  the  fusion  and  collects  the  precious  metals. 


92  NOTES  ON  ASSAYING. 

Endeavor  to  keep  the  oxides  of  the  metals,  such  as  iron,  copper, 
and  manganese,  in  the  condition  of  lower  oxides,  for  the  peroxides 
tend  to  carry  Ag  and  Au  into  the  slag. 

//  base  meialSj  such  as  Cu,  Sby  and  Zn,  are  present  in  the  ore, 
high  litharge  and  as  small  an  amount  of  reducing  agent  as  possible 
should  be  used,  to  avoid  reducing  these  metals.  See  Special 
Methods. 

Class  I. — Fusion  in  the  Muffle.  (See  Assay  of  Ores  for  Lead 
In  regard  to  the  manner  in  which  the  fusion  in  the  muffle  is  con- 
ducted.) 

The  fusions  on  ores  in  Class  I  can  be  made  in  the  muffle  as 
well  as  in  the  pot-furnace.  In  early  days,  in  the  Far  West,  a  pot- 
furnace  fired  by  solid  fuel  was  used  almost  entirely.  At 
present  such  a  furnace  is  very  seldom  seen,  most  assays  being 
made  in  the  muffle.  Since  the  gasoline  and  oil  furnaces, 
especially  the  combination  ones,  have  been  introduced,  one  sees 
many  fusions  made  in  these  crucible-furnaces  as  well  as  in 
the  muffle.  The  pot-furnace  has  the  advantage  over  a  muffle, 
iired  by  solid  fuel,  in  that  a  much  higher  temperature  can  be  ob- 
tained, which  is  very  essential  in  the  fusion  of  some  refractory  ores. 

The  charge  is  usually  made  up  somewhat  as  follows  (use  an 
A  or  B  crucible,  Colorado  form): 

Ore J  A.T. 

Sodium  bicarbonate 15-10  grammes 

Mix  in  the    I  Borax  glass 0-5 

crucible       I  Litharge 60-90 

Algols  (R.P.- 71)    3i 

[Silica  (SiO2) 1-3 

Cover  of  salt. 

In  this  charge  we  aim  to  have  fluxes  sufficient  to  form  a  good 
slag  and  yet  give  a  fusion  which  will  boil  up  but  slightly.  For 
this  reason  the  litharge  is  high,  the  soda  low,  and  borax  glass  is 
used  in  place  of  borax.  Iron  oxides  require  much  SiO2  in  the 
charge,  so  a  variation  in  the  amount  of  either  SiO2,  litharge,  or 
borax  glass  from  that  given  will  generally  make  the  fusion  satis- 
factory. The  following  will  serve  as  an  example  of  an  ore  which 
was  decomposed  in  a  pot-fusion,  but  not  in  a  muffle,  heated  by  coke: 


Mix 

in  the 
crucible 


ASSAY  OF  ORES  FOR  S1LYER.  93 

Ore  2298-5,  consisting  of  hematite  and  some  quartz. 

Ore JA.T. 

Sodium  bicarbonate 15  grammes 

Borax  glass 3 

Litharge 90 

Silica  (SiO2) 3 

lArgols 5        " 

Cover  of  salt. 

Fusion  was  made  in  a  B  crucible  at  the  highest  temperature 
of  the  muffle  for  55  minutes.  The  result  was  a  small  lead  but- 
ton, with  the  slag  completely  full  of  fine  lead  globules.  A  second 
charge  was  fused  for  i^  hours,  but  gave  the  same  result. 

A  charge  identical  in  every  way  was  then  fused  in  a  B  cru- 
cible for  55  minutes  in  a  pot-furnace  heated  by  coke,  and  the 
result  was  a  44-gramme  lead  button  and  a  clean  slag  free  from 
lead  globules.  The  explanation  is  that  the  heat  was  not  suffi- 
ciently high  in  the  muffle-furnace  for  the  character  of  the  charge. 

Class  II.  (Ores  carrying  sulphides,  arsenides,  or  organic 
matter,  i.e.,  ores  which  can  decompose  litharge  with  a  reduction 
of  lead.) — Crucible  assays  of  ores  in  this  class  can  be  made  by/ 
two  methods. 

ist  Method- — In  this  the  reducing  power  of  the  ore  is  first 
determined  by  a  preliminary  fusion  and  the  regular  fusion  charge, 
based  on  this  reducing  power,  figured  out  afterwards  (see  page  103). 

2d  or  Iron  Method. 

Therefore  before  taking  up  the  actual  assay  of  sulphide 
and  arsenical  ores  under  this  class  the  following  experiments 
should  be  carefully  studied  and  considered.  They  all  have 
an  important  bearing  upon  the  assay  of  these  ores,  and  the 
experiments  have  been  carried  out  from  time  to  time  as 
things  came  up  in  the  laboratory  which  suggested  them. 
A  student  commencing  assay  work  seems  to  be  under  the  impres- 
sion that  the  fluxes  used  and  the  amounts  taken  are  chiefly  mat- 
ters of  guesswork.  No  greater  mistake  can  be  made.  All  the 
fluxes  used  have  a  bearing  upon  the  work,  and  if  the  proper 
amounts  are  not  taken,  most  unexpected  results  will  follow, 
and  the  assays  will  be  inaccurate  for  both  the  silver  and  the  gold. 


94  NOTES  CW  ASSAYING. 

Samples  to  be  assayed  constantly  vary  in  composition,  conse- 
quently the  fluxes  and  the  amounts  used  in  the  charge  must 
also  vary.* 

Class  II,  Method  I.  Reducing  Power  of  Ores. — In  taking  up 
this  work,  it  seems  necessary  to  distinguish  between  the  working 
reducing  power  and  the  true  reducing  power  of  an  ore. 

The  working  reducing  power  is  that  by  which  we  can  obtain 
a  satisfactory  lead  button  in  the  regular  fusion  weighing  within 
i  to  4  grammes  of  the  weight  calculated  for. 

The  true  reducing  power  seems  to  be  a  difficult  thing  to 
•determine. 

The  working  reducing  power  can  be  obtained  in  either  of 
two  ways : 

A.  By  the  use  of  the  same  amount  of  sodium  bicarbonate 
•or  carbonate  as  of  ore  used  and  a  large  excess  of  litharge,  i.e., 
40  to  50  times  the  amount  of  the  ore. 

B.  By  allowing  a  certain  amount  of  sodium  bicarbonate  or 
carbonate  to  replace  a  given  quantity  of  litharge. 

The  following  charges  will  serve  as  illustrations. 

PRELIMINARY   FUSIONS. 

In  our  regular  assay  fusion,  the  amount  of  bicarbonate  of 
soda  used  is  generally  the  same  as  the  ore  or  twice  the  ore;  there- 
fore in  the  preliminary  fusion  we  maintain  the  same  ratio. 

Weigh  the  fluxes  out  first  and  place  the  ore  on  top,  then  mix  all 
•in  the  crucible. 

Method  A.     Use  an  E  or  F  crucible. 

Take    2  grammes  of  ore  if  the  quantity  of  sulphides  is  very  large. 
"       3        *'  "  medium. 

"       5        "          "    "  "    "          "        "        "          "  small. 
"      10        "          "    "  "    "          "        "        "          "  very  small. 
"80        "          "  litharge. 

"     same  amount  of  sodium  bicarbonate  as  of  ore  taken. 
"      5  grammes  glass. 

SiO2,  none.  Cover  of  salt  in  each  case.  Make  one  assay  and  fuse  for  8  to  1 2 
minutes. 

The  working  reducing  power  of  any  ore  (except  perhaps  some 
high-grade  copper  ores)  can  be  obtained  by  some  one  of  the 
above  charges.  Less  litharge  can  be  used  in  the  case  of  most  ores, 

*  There  is  a  very  large  field  for  research  work  in  the  analysis  of  slags, 
.especially  from  crucible  work. 


ASSAY  OF  ORES  FOR  SILVER.  95 

but  beginners  will  often  obtain  incorrect  results  by  using  too 
much  ore  and  insufficient  litharge  or  too  much  SiO2.  This  last 
is  therefore  left  out  entirely. 

Method   B.    Use  an  E  or  F  crucible. 

Take  2  grammes  of  ore  if  the  quantity  of  sulphides  is  very  large. 
3        "  "       "         "         "  medium. 

5        "          ""•««  "    "          "        "         "          "  small. 
10        "  "  very  small. 

60        ' '  "  litharge. 

6,  6,  10,  and  20  grammes  of  sodium  bicarbonate  respectively. 
5  grammes  of  glass. 
Cover  of  salt.     Make  one  assay  and  fuse  for  10  to  15  minutes. 

This  method  usually  gives  a  higher  value  for  the  R.P.  of 
an  ore,  especially  on  heavy  sulphuretted  ones,  owing  to  the  increase 
of  the  bicarbonate  of  soda  which  takes  the  place  of  the  extra 
20  grammes  of  litharge  used  in  method  A. 

In  finding  the  reducing  power  of  an  ore,  use  one  of  these 
methods.  Having  determined  the  R.P.,  figure  out  the  charge 
for  the  regular  fusion,  page  103.  Conduct  the  fusion  as  when 
determining  the  R.P.  of  argols  and  charcoal,  only  be  still  more 
careful  that  the  contents  of  the  crucible  do  not  boil  over.  Fuse 
for  ten  to  fifteen  minutes  at  a  high  temperature,  pour  fusion,  and 
weigh  the  resulting  lead  button  upon  the  pulp-balances  to  the 
first  place  of  decimals. 

If  5  grammes  of  ore  were  used  and  the  lead  button  weighs 
5.5  grammes,  the  R.P.  of  the  ore  is  equal  to  i.i. 

The  amount  of  lead  thrown  down  in  the  preliminary  fusion 
is  influenced  by  the  reagents  in  the  charge,  the  relation  of  these 
to  each  other  and  to  the  ore  used,  also  by  the  temperature. 

That  is,  an  incorrect  working  value  may  very  easily  be  ob- 
tained for  an  ore  in  one  of  the  following  ways : 

(a)  By  the  use  of  too  much  silica. 

(b)  By  the  use  of  borax  and  no  sodium  bicarbonate. 

(c)  By  the  use  of  too  little  litharge  or,  what  is  the  same  thing, 
too  much  ore  for  a  given  quantity  of  litharge. 

(d)  By  omitting  the  sodium  bicarbonate. 

(e)  By  an  incorrect  temperature. 

The  following  experiments,  taken  from  the  thesis  of  Messrs. 
M.  Brown,  Jr.,  and  R.  C.  Reed,  of  the  class  of  1904,  illustrate 
these  points  and  are  of  especial  value. 


96  NOTES  ON  ASSAYING. 

The  ores  they  worked  upon  were  grouped  as  follows,  accord- 
ing to  their  R.P.  : 

Sulphides  very  large,  very  high  R.P above  8 

large,  high  R.P 4  to  8 

medium,  R.P i  to  4 

small,  R.P below  r 

(a)  The  effect  of  too  much  SiO2. 

Ore  No.  2420-4. 

Ore,         grammes 3  3  3  3  3 

Litharge,        "          60  60  60  60  60 

Silica,             "          —  2  4  6  8 

Salt cover  cover  cover  cover  cover 

Time  of  fusion,  minutes.  .....  13  10  10  13  13 

Temperature,  degrees  C 1240  1290  1320  1160  1265 

Lead,  grammes 14.72  13.61  n-93  5.70  3.63 

R-p 4-91  4-54  3-98  1.90  1.21 

Ore  No.  2545,  ZnS  and  Other  Sulphides.  Ore  No.  605. 

Ore,  grammes   523  Ore,  grammes     10  3 

Bicarb,  soda,    "52  6  Bicarb,  soda,    "  10          3 

PbO,  "       100        60          50  Litharge,  "          100       120 

SiO2,  "         10          o  o  SiO3,  "  10          3 

Cover  of  salt  in  each  case.  Cover  of  salt. 

Time,  minutes.  ...      12  12  12  Fusion,  25  minutes 

Lead,  grammes.  ..      13     16.66     25.76  Lead  and  matte  =       42.2 

R.P 2.6       8.33       8.58  Lead  =  24 

Working  value  =  8. 45,  i.e.,  the  aver-  Working  value  =  8 

age  of  the  last  two. 

In  five  of  these  fusions  so  much  litharge  combined  with  the 
silica  to  form  lead  silicate  that  not  enough  was  left  to  decompose 
the  ore. 

(b)  The  effect  o)  borax  and  no  sodium  bicarbonate. 

(  PbS 
Ore  No.  2420-4  K  Cu2S 

(  SiO2  and  CaSO4. 

Ore,                grammes 33333 

Bicarb,  soda,       "          —  —  —  6  3 

PbO,                    "         60  60  60  60  60 

Borax,                  "         3  6  9  —  3 

Salt cover  cover  cover  cover  cover 

Time,  minutes n  10  10  13  — 

Temperature,  degrees  C 1265  1200  1225  1330  1345 

Lead,  grammes 11.40  12.57  I3-I3  23.26  18.67 

R.P 3-8°  4.19  4-37  7-75  6-22- 


ASSAY  OF  ORES  FOR  SILVER.  97 

In  this  ore,  owing  to  the  galena  present  in  it,  the  effect  of 
borax  is  to  increase  the  size  of  the  lead  button. 

(c)  The  use  of  too  little  litharge  will  give  an  incorrect  value,, 
especially  if  the  R.P.  is  high;  for  instance,  using  5  or  10  grammes 
of  a  heavy  sulphide  ore,  5  or  10  of  soda,  and  only  60  of  PbO. 

(d)  Omitting  the  carbonate  of  soda.    The  effect  of  this  reagent 
upon  the  size  of  the  lead  button  is  more  marked  than  any  other,, 
and  as  it  is  always  used  in  the  regular  fusion  of  an  ore,  to  omit 
it  in  the  preliminary  is  fatal,  if  the  weight  of  the  final  lead  button 
is  to  be  anywhere  near  the  amount  desired  or  calculated  for. 

In  our  regular  ore  fusion  the  soda  is  either  the  same  amount 
as  the  ore  or  twice  the  amount,  and  for  this  reason  these  propor- 
tions are  maintained  in  the  preliminary  fusion. 

Silicious  ore  carrying  FeS2.     Sulphur  =  3 1.34%.     Through  160  sieve. 

No.  of  Fusion i          2          3  4          5  6  7          8          9 

Ore,  grammes. 5         5         5         5         5         5         5        5         5 

Sodium  carbonate,  grammes.  .     —      —      —     —      —        5       20        5         40 

Litharge,  ft       . .   100     150     200     250     400     100     100  200     100- 

Borax,  «.._______s         __ 

Glass,  «..______      —      5         -__- 

Silica,  "       ..     — 

Cover  of  salt  in  each  case. 

Lead,  grammes 25       26      27       28       39      35       38      39      39, 

R.P 5     5-2     5-45-6     7.0     7.0     7.6  7.8     7.8 

The  R.P.  of  this  ore  is  evidently  7.8,  and  the  fusions  show  that 
a  certain  amount  of  carbonate  of  soda  is  equal  to  so  much  litharge. 

Let  us  see  if  it  can  be  determined  what  reactions  have  taken 
place  in  the  foregoing  fusions  (i  to  9)  or  when  FeS2  and  PbO 
are  brought  in  contact. 

In  Mitchell's  Assaying  we  find  that  FeS2  requires  50  parts 
of  litharge  to  completely  decompose  it,  any  more  than  that  hav- 
ing no  effect  upon  the  size  of  the  lead  button.  Fusion  5  seems 
to  require  80  parts,  and  this  ore  is  not  pure  FeS2. 

1.  FeS2+5PbO  =  FeO+2SO2+5Pb,  that  is,  2S  =  sPb  or  one 
of  FeS2  will  reduce  8.62  lead. 

2.  3FeS2+i6PbO  =  FeO+Fe2O3+6SO2+i6Pb.    HereFeS2re- 
duces  9.2  lead,  or  6S  =  i6Pb. 

3.  2FeS2+uPbO  =  Fe2O3+4SO2+nPb.     Here  FeS2  reduces 
9.48  lead,  or  48  =  uPb. 


98  NOTES  ON  ASSAYING. 

The  ore  carried  31.34   per  cent    sulphur;    therefore    for  5 
grammes  of  ore  in  reaction  No.  i  we  should  have 

8.62X5X31-34 

53-33  =25'3' 

or 


28 
which  is  the  amount  of  lead  reduced  in  fusion  No.  i. 

9-2X5X31.34 

-    -   =27,  or  the  amount  reduced  in  fusion  3. 
oo  *oo 

9.48X5X31.34  ,  .    -  . 

-  =  27.9,  or  the  amount  reduced  in  fusion  4. 

JO'OO 

The  question  now  arises  how  the  39  grammes  of  lead  reduced 
in  some  of  the  other  fusions  can  be  accounted  for.  In  order  to 
obtain  this  amount  of  lead  from  reaction  No.  3,  the  ore  would 
have  to  contain  44.8  per  cent  of  sulphur.  The  large  buttons  of 
lead  must  therefore  be  due  to  something  else,  and  the  carbonate 
of  soda  must  be  responsible  for  it,  for  a  large  amount  of  soda 
apparently  takes  the  place  of  a  certain  amount  of  litharge. 

An  explanation  seems  to  be  that  the  SO2  formed  in  the  re- 
actions given  is  further  oxidized  to  SO3  or  forms  Na2SO4,  which 
is  confirmed  by  finding  sulphates  in  the  slag. 

Na2CO3  breaks  up  by  heat  into  Na2O  +  CO2. 
/.  Na2O+SO2+PbO  =  Na2SO4+Pb, 

or  Na2CO3+  SO2  +  PbO  =  Na2SO4  +  Pb+  CO2. 

In   this   equation  i  S  =  i  Pb  =  i  Na2CO3.     If   the   Na2CO3   is 

completely  changed,  we  shall  haveM    rr>  =  —  ^  =  1.95  grammes  of 

!Na2v^v_/3     100 

lead,  and  5  grammes  of  soda  will  give  9.75  of  lead.  Comparing 
fusion  i  with  6,  and  3  with  8,  we  see  that  the  lead  buttons,  in 
the  fusions  where  soda  is  used,  are  larger  by  practically  this 
amount. 

It  is  very  evident  from  these  experiments  that  if  the  ratio  of 
the  soda  to  the  ore  is  one  to  one  in  the  preliminary  fusion,  it  must 


ASS  A  Y  OF  ORES  FOR  SILVER.  99 

be  one  to  one  in  the  regular  fusion,  otherwise  the  resulting  lead 
button  will  be  quite  different  from  what  is  expected. 
The  following  fusion  also  shows  how  SO3  is  formed. 

(PbS  carrying  about  84%  lead) : 

Ore i  A.T. 

Bicarb,  of  soda 40  grammes 

Borax 15         " 

Litharge 150         " 

Cover  of  salt. 

A  3  5 -minute  fusion  gave  a  lead  button  weighing  97  grammes. 

If  the  reaction  PbS+3PbO  =  SO3+4Pb  takes  place  and  the 
ore  carries  84  per  cent  lead,  then  we  should  expect  to  obtain 
97  grammes  of  lead,  because  by  this  reaction  i  gramme  of  PbS 
reduces  3.46  grammes  of  lead  and  28.28  (PbS  in  ore)  X 3. 46  =  97. 8. 
On  the  other  hand,  if  SO2  was  formed  (2PbO+PbS  =  SO2+3Pb), 
only  a  7 3. 2 -gramme  lead  button  would  be  obtained. 

The  following  are  some  other  tables  showing  the  effect  of  soda : 

Ore  1919.     Through  140.     ZnS  with  very  little  gangue. 

No.  of  Fusion..         229  230  109  no  108 

Ore,  grammes 33333 

Bicarb,  soda,  "      o  3  6  9  3 

Litharge,  "      60  60  60  60  100 

Cover  of  salt  in  each  case. 

Time,  minutes 15  15  15  15  15 

Temperature,  degrees  C 1345  1330  1170  1265       .    1145 

Lead,  grammes 18.34  21.2  24         24.92         22.03 

R.P 6. ii  7.07  8  8.31  7.34 

No.  229  gives  too  low  a  result,  because  no  soda  is  used. 

No.  230     "      "      "  "     "  "       with  an  ore  having  as  high  a  R.P.  as 

this  ore,  if  the  soda  is  the  same  as  the  ore,  the  ratio  of  litharge  to  ore  should  be 
40  or  50  to  i,  whereas  the  ratio  used  is  only  20  to  i. 

Comparing  fusions  108  and  109  it  is  seen  that  3  grammes 
of  soda  takes  the  place  of  more  than  40  grammes  of  litharge. 

The  limit  of  soda  is  apparently  twice  the  ore,  for  the  slight 
difference  in  the  lead  buttons  in  Nos.  109  and  no  may  be 
accounted  for  by  the  difference  in  temperature. 

Fusion  146,  on  page  82,  fixes  both  the  amount  of  soda  and 
litharge  to  use  for  that  particular  ore. 


loo  NOTES  ON  ASSAYING. 

Ore  D.  Mostly  galena,  a  little  pyrite,  and  a  slight  amount  of  gangue,  i.e.,a. 
medium  amount  of  sulphides. 

No.  of  Fusion.  .  182               183               184  185  186 

Ore,                grammes 5                 5                 5  5  5 

Bicarb,  soda,         "      o                5                8  10  15 

Litharge,               "       60              60              60  60  60 

Cover  of  salt  in  each  case. 

Time,  minutes 10               10               n  n  10 

Temperature,  degrees  C 1225           1280           1290  1265  1250 

Lead,  grammes 14.82         20.68         20.66  20.80  21.20 

R-P 2.96           4.14           4.13  4.16  4.25 

This  ore  has  a  much  lower  R.P.  than  the  previous  ones,. 
and  we  find  that  the  same  amount  of  soda  as  ore  gives  prac- 
tically the  same  value  as  when  three  times  the  amount  of  soda, 
is  used.  Where  the  soda  is  omitted  the  R.P.,  as  usual,  is  too  low* 
Owing  to  the  medium  amount  of  sulphides  and  the  fact  that  they 
are  mostly  galena,  60  grammes  of  PbO  are  sufficient  for  5  grammes- 
of  ore  when  5  of  soda  are  used. 

Ore  900.  Silicious  ore  carrying  pyrite  and  a  little  galena.  Small  amount 
of  sulphides. 

No.  of  Fusion. .                 208  174  209  175 

Ore,                grammes 5  5  5  5 

Bicarb,  soda,        "        o  5  8  10 

Litharge,                "        60  60  60  60 

Cover,  of  salt  in  each  case. 

Time,  minutes n  10  10  10 

Temperature,  degrees  C 1320  1280  1160  1305 

Lead,  grammes 8.82  12.98  13.06  13.08 

R.P 1.76  2.60  2.61  2.62 

This  ore  has  a  still  lower  R.P.;  soda  is  still  necessary,  but 
here  a  smaller  amount  than  5  grammes  would  no  doubt  do  for 
5  grammes  of  ore. 

Ore  262.     Very  small  amount  of  sulphides. 

No.  of  Fusion. .          197               198  199  200  136 

Ore,          grammes 10               10  10  10  10 

Bicarb,  soda,    "      o                 5  10  15  10 

Litharge,             "      60               60  60  60  115 

Cover  of  salt  in  each  case. 

Time,  minutes 10               10  10  10  20 

Temperature,  degrees  C 1280           1400  1385  1370  1280 

Lead,  grammes 4.58           5.46  5.40  5.51  6.02 

R-P 46             .55  -54  -55  -60 


ASSAY  OF  ORES  FOR  SILVER.  101 

Owing  to  the  few  sulphides  in  this  ore  we  are  obliged  to  use 
lo  grammes,  and  we  find  an  instance  of  where  nearly  the  cor- 
rect R.  P.  can  be  obtained  simply  with  litharge.  This  is  only 
possible  owing  to  the  very  large  ratio  that  the  litharge  bears  to 
the  sulphides. 

The  foregoing  tables  show  that  when  the  R.P.  of  an  ore  is 
to  be  determined  the  proportions  of  soda  and  litharge  to  ore, 
as  suggested  on  pages  94  and  95,  should  be  used. 

Similar  experiments  with  borax  and  borax  glass  show  that 
its  effect  is,  in  some  cases,  to  diminish  the  size  of  the  lead  but- 
ton, in  others  to  increase  it.  On  ores  carrying  galena,  and  on 
some  others,  the  addition  of  borax  up  to  a  certain  amount  in- 
creases the  size  of  the  lead  button. 

I  prefer  not  to  use  it  in  the  preliminary  fusion. 

Ore  D.     See  page  100 

•Ore,  grammes 5  5                 5                 5                 5 

Borax,       "        o  3                 6                 9               12 

.Litharge,  "        60  60               60               60               60 

Cover  of  salt  in  each  case. 

Time,  minutes 10  10               10               10               10 

Temperature,  deg.  C 1225  1490           1320           1330           1320 

Lead,  grammes 14.82  15-06         15.11         16.67         16.96 

Galena,  carrying  84%  Pb. 

Ore,  grammes 5  5                     5       .# ,            5 

Borax,      "      —  6                    9                     12 

Litharge, "       60  60                   60                    60 

Cover  of  salt  in  each  case. 

Lead,  grammes 13.14  13.51             14.83               14.47 

The  reaction,  PbS+2PbO  =  SO2+Pb,  evidently  has  some- 
thing to  do  with  this,  or  else  the  borax  is  broken  up  into  Na2O-j- 
2B2O3  and  the  Na2O  acts  as  explained  in  the  case  of  sodium 
carbonate. 

(e)  Effect  oj  Temperature. — As  has  been  pointed  out  on  page  86, 
the  size  of  the  lead  button  is  influenced  by  the  temperature. 
The  experiments  of  Messrs.  Brown  and  Reed  seem  to  indicate 
that  when  two  similar  charges,  containing  no  soda,  are  fused  at 
different  temperatures,  the  one  having  the  higher  temperature 
will  give  the  larger  lead  button. 

When  soda  is  present,  however,  an  increase  of  temperature 
diminishes  the  size  of  the  lead  button. 


102  NOTES  ON  ASSAYING. 

Pyrite.  Arsenopyrite. 

Argols.  ...         3  3  Charcoal,    i           i  Ore 3  3  3  3 

Litharge            60  60  60         60  Soda 3  3  6  6 

Glass 10  10  10  10  Litharge..    100  100  50  50 

Cover  of  salt  in  every  case. 

Time,  min.        15  13  15  15                         15  25  15  17 

Temp.,  °C.    935  1155  935  1155                     1010  1120  980  1305 

Lead 28.51  29.84  26.49  27.57                  22.14  19.00  22.2  21.50 

The  effect  of  SiO2,  as  shown  on  page  96,  is  always  to  diminish 
the  size  of  the  button  in  the  preliminary  fusion.  This  is  due  to 
its  combining  with  the  litharge,  leaving  just  so  much  less  litharge 
free.  Its  effect  is  not  so  marked  when  soda  is  present,  for  some 
silicate  of  soda  is  formed. 

The  following  experiments  show  what  effect  sulphides  have 
on  lead  silicates.  A  singulo  silicate  2PbO,SiO2  was  made  by 
fusing  296  grammes  of  PbO  with  40  grammes  of  SiO2.  The 
resulting  silicate  was  pulverized  and  used  in  the  following  fusions. 
(Pot-furnace,  D  crucibles.) 

ZnS  (R.P.='8.3i).  FeS2(R.P.  =  7.8).    , PbS. > 

Ore,                             grammes. .              2^  2^  2\  2\ 

Lead  silicate,                     "                      50  50  50  50 

Bicarbonate  of  soda,        "                      10  10  —  2^ 

Cover  of  salt  in  each  case. 

Time  of  fusion,  minutes 17  15  12  15 

Temperature,  degrees  C 1340  1195  1415  1290 

Lead,  grammes *&-97  17.68  3-67  6.89 

Matte,        " None  None  None  None 

Per  cent  of  the  total  lead  that  the 

ore  could  reduce 91 . 4  90. 7 

A  trisilicate  of  lead  (2PbO,3SiO2)  was  then  made  by  fusing 
198  grammes  of  PbO  with  80  grammes  of  SiO2,  pulverized  and 
used  in  the  following  fusions.  (Pot-furnace,  D  crucible.) 

ZnS  (R.P.  =  8.31).  FeS2(R.P.  =  7.8)    PbS. 

Ore,                        grammes 2  J  2$  2  £ 

Lead  trisilicate,           "        50  50  50 

Sodium  bicarbonate,  "         2^  2$  2$- 

Cover  of  salt  in  each  case. 

Time  of  fusion,  minutes 12  12  13 

Temperature,  degrees  C 1195  1280  1370- 

Lead,  grammes 1.51  None  i  .82 

Matte,       "        4.45  6.10  .11 


ASSAY  OF  ORES  FOR  SILVER.  103 

These  results  show  that  sulphides  will  almost  wholly  decom- 
pose a  singulo-lead  silicate,  and  soda  materially  aids  the  reduction. 
A  trisilicate  is  not  decomposed,  and  it  is  assumed  from  this  that 
silicates  of  lead  higher  in  silica  than  the  trisilicate  are  not  decom- 
posed. 

This  explains  why  the  use  of  too  much  silica  in  a  charge 
results  in  a  matte  (Ore  605,  page  96),  the  incomplete  decomposi- 
tion of  the  ore,  or  both,  for  the  sulphides  are  unable  to  decompose 
the  higher  lead  silicates  with  a  reduction  of  lead,  and  there  is  not 
sufficient  PbO  left  in  the  charge  to  decompose  the  sulphides. 

For  experiments  upon  the  addition  of  SiO2  to  the  regular 
assay  of  ores,  see  pages  106  and  107. 

Class  II.  Regular  Fusion.  (Pot-furnace.)  Conduct  the 
fusions  as  described  under  Class  I,  using  especial  care  where 
much  nitre  is  present  in  the  charge.  If  in  the  preliminary  fusion 
the  amount  of  bicarbonate  of  soda  was  the  same  as  the  ore, 
figure  the  regular  charge  from  the  value  obtained.  If  the  soda 
was  twice  the  ore,  figure  the  regular  charge  from  that  value  and 
keep  the  soda  twice  the  ore  in  the  regular  fusion.  The  amount 
of  PbO,  nitre,  and  argols  to  be  used  will  have  to  be  calculated 
in  the  case  of  each  and  every -ore.  For  the  R.P.  of  argols  take 
the  value  you  find  in  Testing  for  Reducing  Power,  page  83. 

The  following  will  serve  as  examples. 

No.  i.  No.  2.    No.  '3a.  (FeS2  +  PbS  +  SiO2.) 

Suppose  the  preliminary  fusion  on 5  5                   3  grammes  ore 

gave  a  lead  button  weighing 4.5  9.0             12  grammes 

Then  the  reducing  power= 9  1.8               4 

Make  up  the  charges  as  follows,  using  an  E  or  F  crucible : 

Charge No.  i.  No.  2.  No.  30.       No.  36. 

Ore  (SiO2  and  FeS2) i  A.T.  £  A.T.  £  A.T.       £A.T. 

Sodium  bicarbonate 15  gm.  15  or  30  15     or     18 

Borax $    "  55  5              5 

Litharge 60  "  75        50  ico             60 

Argols  (each  gm.  reduces  8  gm.  of  Pb).  . ;      i£  "  — 

Nitre  (KN03) 7  7 

Iron —  — 

Glass —  5       —  10 

or  Silica  (SiO2) o         o  3 

Cover  of  salt  in  each  case. 

•      In  these  examples  of  sulphide  ores  the  object  is  to  decompose 


104 


NOTES  ON  ASSAYING, 


the  ore  and  to  obtain  a  lead  button  weighing  between  25  and  30 
grammes. 

The  soda  is  generally  low,  but  may  be  high,  and  a  little  borax  is 
used  on  account  of  the  metallic  oxides  formed  from  the  decompo- 
sition of  the  sulphides. 

Charge  No.  i. — The  ore  itself  will  reduce  13.1  grammes  of 
lead;  we  desire  a  button  weighing  between  25  and  30  grammes; 
therefore  ij  grammes  of  argols  (R.P.  =  8)  are  added  to  the  charge. 
The  litharge  is  60,  because  the  soda  is  low. 

Charge  No.  2. — The  ore  itself  will  reduce  26.2  grammes  of 
-lead,  so  no  reducing  agent  is  necessary. 

ChargeNo.^a. — The  ore  will  reduce  14.58X4  =  58.3  grammes 
of  lead;  the  button  desired  is,  say,  28;  lead  to  be  oxidized,  30.3. 
One  gramme  of  nitre  oxidizes  4.3  grammes  of  lead  or  its  equiva- 
lent in  sulphides  (see  page  81);  therefore — —  =7  grammes  of 

T"*O 

nitre  are  necessary. 

In  Charges  2  and  3^  the  litharge  is  above  30  grammes,  because 
we  need  an  excess  above  that  called  for  by  the  reducing  power  of 
the  ore.  For  instance,  in  30,  \  A.T.  of  ore  will  reduce  58.3 
grammes  of  lead,  and  this  may  be  obtained  from  62.8  grammes 
of  PbO  (Pb:  PbO  1:58.3  :*).  If  we  used  this  amount  of  PbO, 
we  might  obtain  a  matte  (PbS)  due  to  some  of  the  litharge  com- 
bining with  the  SiO2  and  the  gangue  in  the  ore,  which  would 
leave  insufficient  PbO  to  decompose  the  ore. 

If  just  the  calculated  amount  of  litharge  is  used  a  matte 
is  less  liable  to  form  when  nitre  is  present  in  the  charge  than 
when  it  is  absent. 

That  is,  it  would  be  less  liable  to  form  in  ore  x  than  it  would 
in  ore  y. 


Ore  (R.P.  =  7) \  A.T. 

Bicarb,  of  soda 15  grammes 

Borax 8 

Litharge  (14.58X7  =  102.0)  no        " 

Nitre i8|       " 

Glass 12 

Cover  of  salt. 


Ore(R.P,  =  2) \  A.T. 

Bicarb,  of  soda 15  grammes 

Borax 8 

Litharge  (14.58X2  =  29.1)  31         " 

Nitre — 

Glass — 

Cover  of  salt. 


ASSAY  OF  ORES  FOR  SILVER.  105 

When  it  does  form  it  is  liable  to  give  low  silver  and  gold  values, 
so  it  is  deemed  advisable  to  use  from  15%  to  25%  of  litharge  above 
what  the  R.P.  of  the  ore  calls  jor.  ' 

The  following  ore  will  serve  as  an  example  of  one  giving  low 
results. 

Ore  1530.     Arsenopyrite  and  pyrite  (R.P.  =  7). 


Number  of  Fusion. 

i 

2 

3 

4 

5 

Ore                                    .   i 

fc  A.T. 

i  A.T. 

i  A.T. 

\  A.T. 

i  A.T. 

Bicarb,  soda,  grammes. 

15 

15 

15 

IS 

15 

Borax, 

8 

8 

8 

8 

8 

Litharge,               " 

88 

99 

no 

121 

132 

Nitre,                     " 

i8£ 

i8£ 

18* 

1  8£ 

18* 

Glass, 

9 

10 

12 

13 

15 

Cover  of  salt  in  each  case. 

Gold,  grammes 00150  .00152  -00155  .00156  .00157 

Ounces 3  3-°4  3-i°  3-J2  3.14 

The  R.P.  of  the  ore  being  7,  J  A.T.  calls  for  109  grammes  of 
litharge;  therefore  we  find  that  the  amount  of  litharge  used  was 

as  follows: 

No.  i  2  3                     4                  5 

20  %  10%  Calcu-                 10%               20%  in 

less  than  less  than  lated                in  excess             excess 

the  required  the  required  amount 

amount  amount 

The  nitre  in  these  fusions  not  only  oxidizes  the  sulphides, 
but  also  the  lead,  as  it  is  thrown  down  in  a  fine  condition,  prob- 
ably in  this  way: 

2KNO3  =  K2O+N2O5; 
N206=2NO+30; 
30+3Pb  =  3PbO. 

Charge  $b  is  made  up  by  decreasing  the  litharge  and  increas- 
ing the  soda,  i.e.,  a  certain  amount  of  soda  takes  the  place  of 
litharge  in  decomposing  the  ore.  No  doubt  there  is  some  definite 
ratio  between  them,  so  that  when  the  soda  is  increased  the  litharge 
can  be  decreased.  Whether  this  ratio  will  apply  to  every  sul- 
phide ore  is  doubtful. 

In  using  this  method  care  must  be  taken  that  the  soda  is  kept 
sufficiently  high  and  that  sufficient  litharge  is  used,  for  otherwise 
the  lead  buttons  will  be  too  small  or  a  matte  may  result. 

//  seems  advisable  to  use  not  less  soda  than  ore  in  any  fusion, 


106  NOTES   ON  ASSAYING. 

nor  less  litharge  than  70  or  80  grammes  jor  \  A .  T.  oj  ore  when  the 
soda  is  low  and  the  R.P.  is  4  or  over. 

If  an  ore  carries  a  very  small  amount  of  sulphides  and  has  a 
reducing  power  of,  say,  .2,  do  not  make  up  a  charge  as  follows: 


II 


Ore i  A.T. 

Sodium  bicarbonate 30  grammes 

Borax 5        " 

Litharge 30        " 


i  ° 

*         [Argols  (R.P.  =  10) 3 

Cover  of  salt. 

This  is  incorrect,  for  the  reason  that  the  argols  may  reduce 
all  the  lead  from  the  litharge  before  the  sulphides  in  the  ore  are 
decomposed  by  the  PbO.  Whether  the  ore  carries  a  small  or  a 
large  amount  of  sulphides,  unless  iron  is  present,  some  excess  of 
PbO  must  be  left  in  the  fusion  to  make  sure  that  all  sulphides 
are  decomposed. 

The  following  charge  would  be  correct  and  the  reducing  power 
would  not  have  to  be  determined: 

„        [Ore JA.T. 

£  £      Sodium  bicarbonate 30  grammes 

•S  r§  \  Borax 5 

Litharge 40        " 

Argols  (each  gm.  reduces  10  gm.  of  Pb)     2 

Cover  of  salt. 

Addition  of  Si02  to  a  Fusion. — It  has  been  shown  on  page  96 
that  the  addition  of  too  much  SiO2  to  a  charge  will  result  in  a 
small  lead  button  and  an  incorrect  R.P. 

If  too  much  is  added  to  a  regular  fusion,  the  lead  button  will 
be  too  small  or  smaller  than  that  calculated  for,  and  the  ore  may 
not  be  wholly  decomposed. 

When  the  R.P.  of  an  ore  is  low  it  necessarily  follows  that  the 
sulphides  must  be  small  and  the  gangue  consequently  large. 
Examples  Nos.  i  and  2,  given  on  page  103,  are  of  this  character, 
and  as  60  and  75  grammes  of  litharge  are  used  respectively,  no 


ASSAY  OF  ORES  FOR  SILVER.  107 

SiO2  is  added,  because  the  ores  have  sufficient  gangue  to  prevent 
the  PbO  cutting  into  the  crucibles.  In  example  30  the  ore  has  a 
R.P.  of  4;  therefore  the  gangue  is  not  large,  and  as  100  grammes 
of  PbO  are  used,  3  grammes  of  SiO2  are  added. 

When  the  PbO  is  high  a  larger  amount  of  SiO2  is  necessary 
than  when  the  PbO  is  low;  then,  again,  the  character  of  some  ores- 
admits  the  addition  of  a  much  larger  amount  of  SiO2  to  a  given. 
quantity  of  PbO  than  another  ore  when  the  same  amount  of 
PbO  is  used. 

The  amount  of  soda  in  the  fusion  also  has  an  important  bear- 
ing upon  the  question. 

Just  how  much  SiO2  to  add  is  an  important  question,  and! 
the  following  experiments  were  carried  out  by  Messrs.  Brown. 
and  Reed  to  see  whether  some  definite  rule  could  be  established:: 

Ore  900.     R.P.  =  2.  6,  page  100. 
Ore 


No.  of  Fusion. 

1  80 
i  A.T, 

181 

fc  A.T. 

234 

£  A.T. 

250 

J  A.T.     i 

251 

k  A.T. 

252 
J  A.T., 

,rb.soda,  grammes.  .  .  . 
arse                " 

15 

7? 

3° 

CQ 

15 
60 

ID 
60 

15 
60 

IS 

e,                     " 

/  o 
•j 

J^ 
•I 

2* 

2i 

2t 

a. 

o 

O 

-i 

2 
4 

8 

2 

16 

Cover  of  salt  in  each  case. 

Time  of  fusion,  minutes.  ...           25             25             20             20  21  22- 

Temperature,  deg.  C  .......        1360         1305         1305         1210  1280  i33<>' 

Lead,  grammes  ...........     22.97         23-7        24.6        22.7  19.9  12.6 

The  lead  button  from  No.  250  is  smaller  than  that  from  No* 
234,  showing  the  effect  of  4  grammes  SiO2.  In  251  there  was 
some  matte. 

On  panning  this  ore,  the  gangue  in  J  A.T.  was  found  to  be 
10.3  grammes;  if  we  add  this  amount  of  gangue  to  the  SiO2  added 
and  compare  it  with  the  soda  we  find  the  ratio  as  follows: 

No.   250  .......................  i  soda  :    .98  silica 

251  .......................  i     "     11.22     " 

252  ..............  .........  i     "     :i.7S     " 

Ore,  No.  231.     Mostly  pyrite.     R.P.  =  4.     Gangue,  8.1  grammes  in  i/2  A.T. 

No.  of  Fusion  ......  253  242  243  244  245 

Ore  ........................    £  A.T.  $  A.T.  J  A.T.  }  A.T.  $  A.T. 

Bicarb,  soda,  grammes  .......  15  15  15  15  15 

Litharge,                "       .......  62  62  62  62  62 

Nitre,                     "      .......  8  8  8  8  8 

Silica,                     "       .......  o  6  12  18  20 


io8 


NOTES  ON  ASSAYING. 


Cover  of  salt. 

Time,  minutes 20              20  20 

Temperature,  degrees  C 1345           1330  1200 

Lead,  grammes 22.5           20.6  14.1 


1320 
9.8 


20 

1280 
8-3 


Fusion  No.  242  gave  a  very  little  matte  besides  the  lead. 

Fusions,  Nos.  243,  244,  and  245  gave  a  steadily  increasing 
quantity  of  matte. 

Ratio  of  soda  to  SiO2  added+ gangue  in  ore  =  i  to  .96  in  242. 
"      "     "     "      "        "     +      "       "     "  -i  to  1.37  in  243. 

62 'grammes  of  litharge  were  used,  because  this  is  the  exact 
amount  which  should  decompose  the  ore  if  the  R.P.  is  4  and  the 
other  fluxes  had  no  influence. 

If  we  look  back  to  page  69,  we  find  that  the  ratio  of  SiO2  to 
soda  could  not  be  over  1.7  to  i  or  the  fusions  would  be  thick 
when  silica,  soda,  and  litharge  were  fused  together,  and  in  these 
fusions  60  grammes  of  PbO  were  free  to  combine  with  the  SiO2  and 
make  the  fusions  liquid,  no  ore  being  present.  On  page  67 
fusions  show  that  when  soda  and  silica  are  fused  together  the  ratio 
should  be  2  to  i. 

Judging  from  the  last  two  tables,  when  J  A.T.  of  ore,  15 
grammes  soda  and  60  grammes  litharge  are  used,  the  ratio  of 
silica  (gangue  in  ore  and  silica  added)  to  soda  should  not  be  over 
i  to  i. 

This  certainly  seems  a  safe  ratio  for  most  ores. 

In  order  to  apply  this,  pan  some  of  the  ore  and  make  an  esti- 
mate of  the  amount  of  gangue  in  it.  One  will  find  that  after  a 
•short  time  a  very  close  estimate  can  be  made,  then  judge  the 
amount  of  SiO2  to  add,  taking  also  into  consideration  the  character 
of  the  sulphides  and  the  amount  of  litharge  used.  Some  ores  on 
the  other  hand  require  an  unusual  amount  of  SiO2  to  be  added. 


Ore  1919  through  140.     ZnS  with  practically  no  gangue. 
-.silica  combines  with  the  zinc,  forming  zinc  silicate. 


In  this  instance  the 


No.  of  Fusion  .  .  . 

125 

225 

226 

241 

126 

227 

228 

245 

236 

246 

237 

Ore  A  T 

$ 

| 

} 

| 

| 

f 

1 

* 

* 

* 

^ 

1  5 

1  5 

15 

2O 

2O 

20 

20 

20 

20 

30 

Litharge,           

150 
15 

ISO 
o 

15° 
o 

ISO 
O 

110 
O 

110 
O 

ITO 
0 

110 

6 

110 

0 

110 
0 

70 
0 

Nitre  '        •«    

22 

22 

22 

22 

22 

22 

22 

22 

22 

22 

22 

Silica',         "    

4 

8 

12 

14 

2 

4 

8 

8 

14 

30 

0 

Cover  of  salt  in  all  fusions. 


30 

35 

33 

35 

3° 

35 

32 

35 

35 

35 

35 

Temperature,  degrees  C  
Lead,  grammes  

118-5 
35.8o 

1385 
?6   ^ 

1305 

28.  T 

1305 
27.6 

137° 
24.9 

1305 
26.4 

1360 
28 

34-3° 

1305 
28.  S 

21 

1320 
24   5 

ASSAY  OF  ORES  FOR  SILVER.  109 

All  these  fusions  were  perfectly  liquid  and  there  was  no  sign 
of  a  matte.  Attention  is  called  to  the  increase  in  size  of  the  lead 
buttons  when  borax  is  used  on  this  ore  (fusions  125  and  245). 

It  is  seen  from  these  fusions  that,  if  the  working  reducing 
power  of  an  ore  is  obtained  correctly,  and  the  fluxes  in  the  regular 
fusion  used  in  the  proper  ratio,  the  resulting  lead  button  will 
come  out  almost  exactly  as  calculated. 

The  following  show  how  close  they  often  come : 

Ore i  A.T.  J  A.T.  i  A.T.  |  A.T. 

Bicarb,  soda,  grammes 15  15  15  15 

Borax,                     "        o  o  o'  7 

Litharge,                 "        65  65  65  65 

Nitre,                      "        9  9  9  9 

Si02,                       "        2  4  7  7 

Cover  of  salt  in  each  case. 

Time,  minutes 20  -20  20  20 

Lead,  grammes 26.1  26.5  26.9  26.1 

Class  II.  Iron  Method.  (See  also  page  133.) — In  this  method 
the  NaHCO3  or  Na2CO3  must  be  two  or  more  times  the  ore  used. 

Litharge  must  not  be  over  30  grammes. 

An  excess  of  iron,  must  be  present. 

The  fusion  is  conducted  as  described  under  Class  I. 

This,  in  my  experience,  has  proved  a  most  excellent  method 
on  ores  which  do  not  contain  arsenic,  antimony,  or  copper.  It 
saves  a  preliminary  fusion,  and  a  lead  button  of  the  proper  size 
for  cupelling  can  always  be  obtained. 

With  ores  containing  antimony  or  copper  a  large  amount  of 
litharge  is  necessary,  in  order  to  oxidize  these  impurities  and 
either  volatilize  or  slag  them;  for  this  reason  the  iron  method, 
in  which  only  a  small  amount  of  litharge  can  be  used,  is  not 
recommended. 

Arsenical  ores  can  be  assayed  by  this  method,  but  special  pre- 
cautions have  to  be  used  and  they  will  be  taken  up  later.  The 
ore  under  example  30  (page  103),  which  has  a  R.P.  of  4,  may  be 
also  assayed  with  the  following  charge. 


NOTES  ON  ASSAYING. 

Ore JA.T.     (FeS2+PbS  +  SiOa.) 

Bicarb,  soda .  .  30  grammes  (always  twice  the  ore  at  least) 

,g      Borax 8         " 

0      Litharge 30       " 

Argols none 

Nitre none 

•8          o-i- 

g       bmca 4  grammes 

or  Glass ....    20 
One  spike  or  nails  (twenty penny)  3,  point  down,  each  of  which 
weighs  about  17  grammes. 
Cover  of  salt. 

In  this  method  an  ore,  like  the  one  just  given,  is  decomposed 
partly  by  the  litharge  and  partly  by  the  iron  as  follows: 

FeS2+  sPbO  =  5Pb+  2SO2+  FeO ; 


We  also  have  the  iron  acting  on  the  litharge  and  lead  silicates. 
that  may  be  formed  or  that  are  present  in  the  fusion: 


2PbO,SiO2+  2Fe  =  2FeO,SiO2+  2Pb. 

The  ore  will  be  perfectly  decomposed  and  the  resulting  lead 
button  will  weigh  between  25  and  28  grammes,  provided  the 
ore  contains  no  lead  minerals.  Practically  all  the  lead  com- 
pounds in  the  fusion  will  be  reduced  to  metallic  lead,  and  it  is 
owing-  to  this  fact  that  the  litharge  must  not  be  over  30  grammes, 
if  we  wish  to  avoid  scorifying  the  resulting  button.  If  an  ore 
carries,  for  instance,  50  per  cent  of  lead  in  the  form  of  galena, 
either  less  than  J  A.T.  of  ore  must  be  used  or  the  charge  made 
up  in  exactly  the  same  way,  and  the  litharge  diminished  from  30 
to  20  grammes. 

The  resulting  button  from  this  fusion  will  weigh  about  25 
grammes,  18  grammes  coming  from  the  litharge  and  7  from  the 
galena  in  the  ore. 


ASSAY  OF  ORES  FOR  SILVER. 


Ill 


Students  always  ask  the  question,  "When  is_iroiL_iiecessary 
in  a  fusion?"  The  answer  is,  when  30  grammes  of  litharge  will 
not  decompose  the  ore  taken  and  leave  some  litharge  in  excess. 

For  Instance,  take  the  two  following  ores: 


Ore(FeS2) £  A.T.(R.P.: 

Bicarb,  soda 30  grammes 

Borax 8          " 

Litharge 30          " 

Argols none 

Iron none 

Cover  of  salt. 
Lead  button 22 


Ore(FeS2) i  A.T.  (R.P.  = 

Bicarb,  soda 30   grammes 

Borax 8          " 

Litharge 30 

Argols none 

Silica 2-3       " 

Iron  nails  (aopenny)  3 

Cover  of  salt. 

Lead  button 27 

In  (e)  30  grammes  of  litharge  will  not  decompose  the  ore  and 
leave  any  excess,  so  we  put  in  iron.  If  we  leave  out  the  iron, 
a  lead  button  and  a  lead  matte  will  be  the  result. 

In  (/)  30  grammes  of  litharge  will  decompose  the  ore  and 
leave  a  little  litharge  in  excess,  so  we  need  no  iron. 

If  an  ore  is  just  on  the  line,  as  one  might  say,  for  instance, 
if  it  has  a  R.P.  of  2  and  carries  no  lead,  then  either  of  the  following 
charges  would  be  correct: 


Ore i  A.T.  (R.P.  =  2) 

Bicarb,  soda 30  grammes 

Borax 8         " 

Litharge 30         " 

Argols none 

Silica....- 2-3        " 

Iron  nails (2 openny)..  3         " 

Cover  of  salt. 

Lead  button 27 


Ore £  A.T.  (R.P.  = 

Bicarb,  soda 30  grammes 

Borax 8 

Litharge 40  to  50         ' ' 

Argols none 

Iron none 

Cover  of  salt. 

Lead  button 29 


If,  in  the  last  four  examples  given,  i  A.T.  of  ore  was  taken 
instead  of  J  A.T.,  then  iron  would  be  necessary  in  all  four  cases, 
the  soda  would  have  to  be  60  and  the  litharge  30  grammes. 
If  we  took  i  A.T.  of  a  galena  ore,  carrying  50  per  cent  of  lead, 
the  soda  would  be  60  and  the  litharge  15  grammes. 

Many  assayers  object  to  the  use  of  iron,  claiming  that  it  is 
liable  to  form  a  matte  with  consequent  inaccurate  results,  h, 
matte  will  never  be  formed  if  an  excess  of  alkali  flux  is  used, 
for  any  iron  matte  formed  will  dissolve  in  the  alkaline  slag. 
The  following  experiments  show  what  takes  place  in  two  fusions, 
wherein  there  is  a  sufficiency  of  alkaline  flux  in  one  case  and 
an  insufficiency  in  the  other. 


Ill 


NOTES  ON  ASSAYING. 


The  ore  in  each  case  consisted  largely  of  FeS2  and  contained 
39.56  per  cent  of  sulphur.  The  reducing  power  was  about  8. 
Each  charge  was  fused  40  minutes. 


(*). 

Ore i  A.T. 

Bicarb,  soda 30  gm. 

C.P.  litharge 30     " 

Glass 15  " 

Iron  nails  (2openny)...  4     " 

Borax  glass  cover 10     " 


60 

Ore i  A.T. 

-p.-.      i   Bicarb,  soda 30  gm. 

C.P.  litharge 30    " 

[  Glass 15    " 

Iron  nails  (20penny)  ..  4    " 

Borax  glass  cover 10    " 


The  following  results  were  obtained: 


Slag 60  grammes 

Matte  (FeS,  a  little  PbS 
and  alkaline  sulphide)..     23^ 

Lead 24^ 

Crucible  and  iron  and  flux 

before  fusion 685 

after  fusion 665 

Loss 20 

Iron  nails  before  fusion. . .     64 
"       ' '     after  fusion.  ...    43 

Loss  of  iron.. .  ,21 


Slag .-    65  grammes 

Matte .  none 


Lead 26 

Crucible  and  iron  and  flux 

before  fusion 662 

after  fusion 642 

Loss 20 

Iron  nails  before  fusion.  .  .    63 
"       ' '     after  fusion 49 

Loss  of  iron 14 


The  reason  no  matte  was  obtained  in  (y)  was  owing  to  the 
ratio  of  the  soda  to  the  ore  taken. 

If  the  soda  in  (x)  was  increased  to  60  grammes,  no  matte 
would  be  obtained.  The  slag  from  (x)  contained  6.73  per  cent 
of  sulphur,  practically  all  as  sulphide;  that  from  (y)  contained 
7.63  per  cent  of  sulphur,  practically  all  as  sulphide.  When 
the  slag  was  treated  with  HC1,  in  both  cases  it  gave  off  H2S 
strongly.  A  large  percentage  was  soluble  in  water.  In  fusion 
(x)  about  8  per  cent  and  in  fusion  (y)  about  14  per  cent  of  the 
sulphur  disappeared,  probably  as  SO2;  the  remainder  was 
undoubtedly  combined  with  the  iron  as  sulphide  of  iron  and  as 
a  double  sulphide  of  iron  and  soda,  which  was  held  in  solution 
by  the  large  excess  of  the  alkali  flux  used.  Some  of  this  double 
sulphide  of  the  iron  and  alkali  was  in  the  matte  in  fusion  (#), 
for  on  standing  some  months  this  matte  fell  to  pieces. 

If  arsenic  had  been  present  in  this  ore,  an  iron  speiss  would 


ASSAY  OF  ORES  FOR  SILVER.  113 

have  resulted  from  both  fusions,  with  the  charges  given,  unless 
great  care  had  been  taken  with  the  temperature  at  which  the 
fusions  were  conducted.  This  question  is  taken  up  under  the 
assay  of  ores  for  gold. 

It  will  be  noticed,  in  all  the  fusions  so  far  given,  that  iron 
and  nitre  are  never  used  in  the  same  charge;  in  other  words,  if 
the  R.P.  of  an  ore  is  determined,  the  charge  is  made  up  as 
described  on  page  103.  If  this  preliminary  fusion  is  not  made 
and  the  iron  method  is  used,  then  the  nitre  is  left  out. 

This  raises  the  question  of  whether  iron  and  nitre  can  or 
should  be  used  in  the  same  fusion.  In  the  rush  of  a  busy  assay 
office  there  is  not  time  to  determine  the  reducing  power  of  each 
sulphide  ore,  so  in  the  case  of  ores  where  arsenic  is  present  or 
suspected  an  assayer  will  use  both  iron  and  nitre  in  the  same 
fusion.  Personally  I  do  not  believe  in  this.  An  assayer  in 
the  West  writes  me:  "On  heavy  iron  concentrates,  analyzing 
about  40%  sulphur,  36%  iron,  and  10%  SiO2,  with  small  amounts 
of  arsenic,  antimony,  zinc,  and  lead,  I  use  the  following : 


Ore i  A.T. 

Litharge 30  grammes 

Silica 3 

Nitre 4        " 

Flour 2$      "         (  Sodium  bicarbonate.  ...   i  part 

lo-gm.  crucible,  about  f  full  of  a  mixed  flux.  •<  Potassium  carbonate.  . .   i     " 

'  Borax  glass 2  parts 

Four  tenpenny  nails  and  a  cover  of  flux. 


For  lighter  sulphides  the  nitre  is  cut  down,  still  using  enough 
flour  for  a  reducing  agent." 

Whether  an  iron  speiss  will  result  from  a  fusion  like  the 
above  depends  upon: 

i  st.  The  percentage  of  arsenic  in  the  ore. 

2d.  The  temperature  at  which  the  fusion  is  conducted. 

3d.  The  amount  of  alkali,  i.e.,  soda  or  potash,  in  the  charge. 

If  very  little  arsenic  is  present  in  the  ore,,  no  speiss  may 
result,  even  with  so  small  an  amount  of  nitre  as  4  grammes; 
but  if  an  ore  is  highly  arsenical,  a  speiss  will  be  very  liable  to 
form. 


114  NOTES   ON  ASSAYING. 

For  the  use  of  iron  with  arsenical  ores  and  experiments  thereon, 
see  Assay  of  Ores  for  Gold,  pages  137  to  139. 

The  great  advantage  of  the  iron  method  is  that  we  are  always 
sure  of  obtaining  a  lead  button  of  the  proper  size  for  cupellation 
and  nitre  is  not  used  in  the  fusion.  This  appears  to  be  a  very 
strong  point  in  its  favor,  especially  in  the  assay  of  ores  for  silver, 
for  I  am  confident  that  in  the  case  of  certain  ores  the  use  of  much 
nitre  in  the  fusion  is  the  cause  of  low  results. 

The  following  fusions  will  illustrate  my  meaning. 

Ore  (R.P.  4.8) i  A.T.  |  A.T. 

Bicarb,  of  soda 15   grammes  30  grammes 

Borax 5  8         " 

Litharge 90         ' '  30        "" 

Silica 3  3 

Nitre 1 1  Iron  nails  4 

Cover  of  salt.  Cover  of  salt. 

Silver  and  gold 28.8  oz.  3 


Ore |  A.T. 

Bicarbonate  of  soda 30  grammes 

Borax 10          *' 

Litharge 25          ' ' 

Si02 3 

Iron  nails  (2openny).  ...       4 

Cover  of  salt. 

Silver  and  gold 67 .  i  oz. 


(a)   Ore  was  PbS  and  ZnS. 

Ore  (R.P.  =  7) J  A.T. 

Bicarbonate  of  soda 15   grammes 

Borax 10 

Litharge 140         ' ' 

Nitre 20          " 

Si02 6 

Cover  of  salt. 

Silver  and  gold 63 . 2  oz. 

For  this  reason  it  seems  advisable  to  avoid  the  use  oj  nitre 
in  the  assay  oj  ores  for  silver,  and  therefore  I  recommend,  when 
ores  have  a  high  R.P.  and  the  iron  method  can  be  used,  a  charge 
.like  (b)  rather  than  one  like  (a).  If  in  (a)  we  took  only  Vio  A.T. 
of  ore  and  made  up  a  charge  on  that  basis  no  nitre  wrould  be 
needed,  but  this  would  do  away  with  the  advantage  of  the  cru- 
cible assay  which  enables  us  to  use  large  amounts  of  ore.  When, 
however,  the  R.P.  is  not  high  the  use  of  nitre  may  be  avoided 
by  taking  such  an  amount  of  ore  and  no  more  as  will  give  us 
a  lead  button  of  just  the  size  desired.  For  instance,  3/io  A.T. 
could  be  taken  where  an  ore  has  a  R.P.  of  3. 

In  any  case,  whether  in  assaying  ores  for  silver  or  for  gold 
or  for  both,  if  the  ores  contain  sulphurets  we  must  either  have 


ASSAY  OF  ORES   FOR  SILVER.  11$ 

ran  excess  of  iron  present  or  an  excess  of  an  oxidizing  agent, 
for  otherwise  the  silver  and  gold  may  remain  in  the  slag  as  a 
double  sulphide  of  the  metal  to  be  determined  and  the  alkali 
used  as  a  flux. 

Large  amounts  of  alkali  or  carbonate  tend  to  carry  sulphur 
and  arsenic  into  the  slag,  and  they  will  remain  there  in  com- 
bination with  the  alkali  or  carbonate  if  the  heat  is  kept  low. 
If  the  heat  is  high,  they  will  tend  to  be  removed,  especially  if 
iron  is  present  in  the  fusion.  (See  fusions  on  page  138.) 

Class  II.  Fusion  in  the  Muffle. — With  ores  of  this  class  the 
fusions  can,  in  many  cases,  be  made  in  the  muffle,  but  it  must 
be  borne  in  mind  that,  owing  to  the  use  of  nitre  in  one  method 
•and  the  use  of  high  soda  in  the  method  in  which  iron  is  used,  the 
iusions  are  very  liable  to  boil  over. 

Effect  of  Temperature. — In  the  case  of  certain  sulphide  ores, 
as  in  the  case  of  certain  oxide  ores  of  Class  I,  it  is  very  difficult 
to  obtain  sufficient  heat  in  a  muffle-furnace,  fired  by  coke,  to 
make  a  good  fusion  and  have  the  slag  free  from  lead.  The  same 
fusion  carried  on  in  a  pot-furnace,  heated  by  coke,  gives  perfectly 
satisfactory  results,  so  it  must  be  only  a  question  as  to  temperature. 

Ore  255.  Pyrite  and  a  very  little  chalcopyrite  and  galena  in  a  quartz  gangue. 
R.P.  =  2.7. 


0 


No.  i.  No.  2. 

Ore £  A.T.  }  A.T. 

Sodium  bicarbonate 10  grammes  10  grammes 


Borax  glass 8 

Litharge 100        ' '  100        ' ' 

Nitre 2         "  2 

Glass 10        "  10        " 

Cover  of  salt.  Cover  of  salt. 

Fusion  No.  i  was  made  in  the  muffle  at  its  highest  tempera- 
ture, and  it  was  very  hot,  for  40  minutes.  The  resulting  lead 
button,  weighing  27  grammes,  dropped  away  from  the  slag,  show- 
ing that  the  fusion  had  been  too  long.  The  button  was  brittle 
on  top,  indicating  a  little  matte  and  the  slag  had  some  lead  in  it. 

Fusion  No.  2  was  for  40  minutes  in  a  pot-furnace  and  every- 
thing was  satisfactory.  The  lead  button  weighed  25  grammes, 
was  soft  and  malleable,  and  no  matte  was  present.  The  slag  was 
.perfectly  free  from  lead. 


no  NOTES  ON  ASSAYING. 

EFFECT  ON  SIZE  OF  LEAD  BUTTON. 

A.  B.                           C. 

Ore J  A.T.  \  A.T.                      \  A.T. 

Bicarb,  soda. ...     10    grammes  10    grammes            10    grammes 

Borax  glass 10  10          "                   10          " 

Litharge 100          "  100          "                 100          " 

Nitre 11.8      "  n.8      "                  n.8      " 

Silica 2          "  2          "                    2          " 

Salt                           cover  cover                         cover 

Fusion 50  min.  50  min.                    50  min. 

Lead 19 . 2  grammes  22 . 9  grammes        26. 4  grammes 

A  was  in  the  front  part  of  the  muffle  and  the  coolest. 

B     "    "    "    middle"     "  "        "        "     hotter  than  A. 

C     "    "    "    back      "    "  "       "        "     the  hottest. 

Ores  Containing  Organic  Matter. —  Ores  carrying  much 
organic  matter,  graphitic  shale  or  graphite  may  cause  much, 
trouble  in  crucible  fusions.  Their  presence  is  indicated  by  the 
fusion  puffing  up,  a  crust  forming  on  top  with  flames  burning 
over  it  and  the  charge  pouring  thick  and  pasty. 

Substances  of  this  character  are  not  adapted  to  the  iron 
method  and  should  have  the  reducing  power  determined  as  ia 
the  case  of  sulphide  ores.  If  the  R.P.  is  low,  a  fusion  can  be 
made  as  in  the  case  of  these  ores.  If  the  R.P.  is  very  high  and 
the  substance  poor  in  silver,  it  is  better  to  roast  it  first  (see  page  132) 
and  then  fuse  it,  for  by  so  doing  a  large  amount  can  be  used. 
If  the  R.P.  is  high  and  the  substance  fairly  rich,  an  assay  can 
be  made  as  in  the  following  instance: 

Residue  from  a  zinc  retort.      (R.P.  =  12.) 

Ore Ko  A.T. 

Bicarb,  soda,  grammes 15 

Borax  glass,            "       10 

Litharge,                 "       130 

Nitre,                       « ' 20 

Silica,                       "       4 

Cover  of  salt. 

A  fusion  of  this  sort  boils  violently,  owing  to  the  presence 
of  the  nitre  and  organic  matter  and  great  care  must  be  used 
in  conducting  it. 

Size  of  Lead  Buttons. — In  all  the  crucible  work  it  has  been 
advised  to  have  the  resulting  lead  button  weigh  between  25  and 


.     ASSAY  OF  ORES  FOR  SILVER.  II? 

30  grammes.  The  reason  for  this  is  that  a  button  of  this  size  is 
more  likely  to  collect  all  the  precious  metals  than  a  button  of  a 
.smaller  size.  I  do  not  mean  by  this  that  small  buttons  or  buttons 
up  to  1 8  grammes  may  not  collect  all  the  silver  and  gold,  for  they 
•can  and  do  in  most  cases.  But  in  many  cases  they  do  not,  and 
the  following  will  serve  as  examples.  In  all  these  fusions  every 
endeavor  was  made  to  keep  everything  connected  with  the  differ- 
ent fusions  as  nearly  identical  as  possible  except  the  size  of  the 
lead  button. 

Ore  carrying  AgCl.     (R.P.  =  1.3.) 

Lead  button,  grammes 3  7  21  31 

Silver  and  gold,  ounces H55-6  1217.6  1247.8  1254.2 

Two  assays  on  an  ore  as  rich  as  this  may  perhaps  vary  the 
amount  that  the  last  two  assays  disagree: 

Ore  No.  144. 

I,ead  button,  grammes 8^  n£  23  30 

Silver  and  gold,  ounces 38.79  42.7  53-6a  55.7 

Ore  No.  207.     (R.P.=  i^.) 

X,ead  button,  grammes 8  :6  19  28 

Cold,  ounces i.i  1.37  1.4  1.51 

Ore  No.  no.     (R.P.  less  than  i.) 

Lead  button,  grammes 9  13  25 

Silver  and  gold,  ounces i.i  1.7  1.8 

The  loss  in  cupelling  lead  buttons  weighing  from  25  to  30 
grammes  is  no  doubt  slightly  larger  than  in  cupelling  those  weigh- 
ing from  15  to  2.0,  but  the  loss  is  nothing  like  the  difference 
shown  in  the  foregoing  examples  by  having  the  lead  buttons  of 
insufficient  size  to  collect  all  the  precious  metals  in  a  fusion. 

It  will  generally  be  observed  that  when  especially  nice  work 
is  being  carried  on,  the  lead  buttons  will  weigh  between  25  and 
30  grammes. 

Dusting  of  Ores. — Certain  ores,  when  commencing  to  fuse 
in  a  crucible,  and  sometimes  even  before,  have  a  tendency  to  dust. 
This  can  be  easily  seen  by  noticing  the  cover  of  salt  as  well  as  the 
rim  and  cover  of  the  crucible,  which  will  be  covered  with  the 
fine  ore  blown  up  from  little  holes  in  the  charge.  Serious  losses 
may  occur  in  this  way,  and  in  the  case  of  certain  ores  it  is  very 
'difficult  to  account  for  the  phenomenon. 


n8  NOTES  ON  ASSAYING. 

The  following  precautions  may  in  many  instances  prevent  it  r 

1.  After  having  placed  the  crucible  in  the  fire,  on  no  account 
touch  or  disturb  it  until  the  contents  have  fused  or  sintered. 

2.  Placing  a  heavy  cover  of  borax  glass  on  top  of  the  charge.. 

3.  Making  a  very  quick  fusion. 

SPECIAL   METHODS. 

Silver  in  Copper  Ores.  Crucible  Fusion. — Ores  and  products, 
which  contain  a  high  percentage  of  a  metal  like  copper,  anti- 
mony, or  any  metal  which  is  liable  to  be  reduced  and  pass  into 
the  lead  button  in  the  crucible  assay,  are  generally  assayed  by 
scorification  or  some  wet  process.  Some  ores  carrying  up  to 
25  or  30  per  cent  copper  can  be  assayed  satisfactorily  by  the 
crucible  method.  If  the  percentage  is  above  this  and  as  much 
as  J  A.T.  of  ore  is  taken,  it  is  difficult  to  prevent  so  much  copper 
going  into  the  lead  button  that  a  scorification  of  the  button  is 
unavoidable. 

To  test  an  ore  for  copper,  boil  a  little  of  it  in  HNO3  or  aqua 
regia,  cool,  and  make  strongly  alkaline  with  ammonia.  A 
deep  blue  color  indicates  the  presence  of  copper.  Much  nickel 
may  give  a  color  somewhat  similar. 

The  following  fusions  made  on  an  ore  carrying  12  J  per  cent 
of  copper  and  consisting  of  pyrite,  pyrrhotite,  and  chalcopyrite> 
with  a  R.P.  of  5^,  will  show  the  method  to  follow: 

Pot-furnace,  G  crucible. 

Ore \  A.T.  \  A.T. 

Sodium  bicarbonate.    20  grammes  20  grammes 

Borax  glass 10        "  10 

Litharge 150        "  150        " 

Nitre 13        "  13 

Silica.. 6       "  6       " 

Cover  of  salt.  Cover  of  salt. 

Fusion 50  minutes  50  minutes  at  rather  low  tem- 

perature 

Lead  (from  both  fu- 
sions cupelled  di- 
rectly)    23  grammes  25  grammes  (quite  soft) 

Cupels  a  little  dark,  indicating; 
a  little  copper  oxide 

Ag 2.42  ounces  2.64  ounces 

Au .26       "  .26      " 


ASSAY  OF  ORES  FOR  SILVER. 

It  will  be  seen  that  the  object  in  these  charges  was  to  have 
the  litharge  extremely  high  in  order  to  oxidize  the  copper  and 
drive  it  into  the  slag. 

The  silica  was  also  kept  high,  that  it  might  assist  in  slagging 
the  copper.  After  pouring,  the  top  of  both  fusions  was  very 
blue,  indicating  sulphate  of  copper  and  some  chloride  of  copper 
in  the  cover  of  salt. 

The  slag  itself  was  deep  red,  due  to  the  Cu2O  carried  there  by 
the  litharge. 

Copper  mattes  may  be  assayed  in  this  manner  using  J  A.T. 
or  -fa  A.T.  This  is  a  larger  amount  than  can  safely  be  used 
in  a  scorifier,  which  is  certainly  an  advantage  if  the  matte  carries, 
only  a  little  silver.  Then  again  these  amounts  will  often  bring 
down  a  lead  button  of  just  the  desired  size,  so  that  the  use  of 
nitre  is  avoided. 

If  the  ore  is  an  oxide  ore,  either  native  or  due  to  the  roasting 
of  a  sulphide,  and  contains  copper,  the  charge  is  made  up  as 
follows  and  can  be  done  either  in  the  muffle-  or  the  pot-furnace. 
The  following  ore  is  considered  as  having  no  oxidizing  power: 

Ore 5  grammes  ^  A.T. 

Sodium  bicarbonate 5         "  15       grammes 

Borax 2         "  5 

.*  g     Litharge 60         "  90-1 10       " 

Argols  (R.P.  10) 2±       "  2\ 

Silica 1-2        "  3-5  " 

Cover  of  salt.  Cover  of  salt. 
The  temperature  should  be  medium. 

If  the  ore  has  an  oxidizing  power,  then  this  must  be  deter- 
mined; for  if  too  much  reducing  agent  is  used,  the  lead  button 
will  be  too  large  and  will  probably  contain  considerable  copper 
brought  down  at  the  same  time  as  the  lead. 

If  the  resulting  lead  button  is  hard  or  brittle,  add  sufficient 
lead  to  make  the  weight  60  grammes  and  scorify  in  a  2f"  or  3" 
scorifier.  As  soon  as  the  lead  begins  to  drive  add  a  little  fine 
silica  and  scorify  at  a  low  temperature,  as  described  under  Copper 
Mattes,  Scorification  Assay. 


120 


NOTES  ON  ASSAYING. 


The  following  interesting  data  in  regard  to  the  crucible  assay 
of  a  cupriferous  silver  and  gold  ore  were  obtained  by  Mr.  W.  W. 
Trowbridge  of  the  class  of  1904.  The  ore  was  chiefly  chalco- 
pyrite  and  showed  on  analysis: 

Copper 24% 

Sulphur.. 35-5% 

Lead 3-5% 

Silver 51 . 6  oz. 

Gold 3 .  i  oz. 

If  we  satisfy  the  copper  with  sulphur  to  form  Cu2S  and  the 
remaining  sulphur  with  iron  to  form  Fe2S3,  the  iron  would  be 
34.37%,  leaving  2.63%  for  the  gangue  matter. 

R.P.  OF  THE  ORE,   SHOWING  EFFECT  OF   DIFFERENT  REAGENTS. 


No.  of  Fusion  .  . 
Ore,  grammes  
Soda,  

i 
3 

2 

3 

3 
3 

4 
3 

5 
3 
3 

6 
3 
3 

7 
3 
3 

8 
3 
3 

10 

3 
3 

r 

I  2 
2 
2 

19 
2 

5 

20 

2 

5 

21 
2 

0 

Litharge  

60 

60 

90 

90 

60 

90 

90 

120 

90 

90 

90 

40 

60 

106 

itre,  
Silica,  

— 

— 

3 

— 

— 

3 

3 

3 

— 

• 

1 

— 

— 

— 

Cover  of  salt  in  each  case. 


Time  fusion,  min.  .  . 

Temp.,  deg.  C 

Lead,  grammes 


24 
680 
9.2 


12 

870 

12.8 


14 

860 
13-4 


12 

1040 
14 


15 
910 


760 
19-7 


900 


15 

660 

21.5 


23.5 


12 

1270 

18.6 


1 8 


14.7 


Appearance  of  button:    fusions  i  to  10,  brittle;    n,  12,  19,  20,  and  21  good. 

Slag:  fusions  i  to  4,  black;  5  to  8,  dark  brown;    10  to  12,  black;    19,  20,  reddish;  21 

black. 
Salt:  fusions  i  to  12,  green;   19,  brown;  20,  yellow;   21,  green. 


Depending  upon  the  reagents  used,  the  R.P.  varies  from  3.06 
to  9,  and  the  latter  is  considered  the  working  R.P. 

The  fusions  again  show  how  absolutely  essential  is  the  pres- 
ence of  sodium  carbonate. 


ASSAY  OF  ORES  FOR  SILI/ER. 


121 


REGULAR  ASSAYS,    SHOWING  THE   EFFECT    OF   DIFFERENT   RF- 
AGENTS   UPON   THE   SLAGGING   OF    THE    COPPER. 

No.  of  Fusion . . 
Ore  grms. 

Bicarb,  soda 
Borax 
Litharge 
Nitre 

Silica                 "...—        —  —        —       1.5       1.5       i-5       i-5 

Salt cover   cover   cover  cover   cover   cover   cover   cover  cover 


18 

28 

17 

35 

36 

15 

16 

25 

30 

is....   3 

3 

10 

10 

10 

10 

IO 

10 

IO 

•••   5 

5 

13 

13 

13 

IO 

IO 

IO 

IO 

...  50 

5° 

70 

70 

70 

IIO 

IIO 

IIO 

IIO 

...   4 

4 

14 

14 

14 

14 

14 

14 

14 

Time  of  fusion,  min.  .     15       14 


16 


high  15 

low    10         a 


27 


23 


Temperature,  deg.  C.     770     mo     1000     1090     AifVJW     1500     1060       820     1500 

Color  of  salt pink     red       pink  reddish  brown  yellow  yellow   —         — 

Weight  of  lead 10.6     10.6     26.3     28.5     23.4     25.9     26.9 


Gold,  ounces 3 . 09 

Silver,     "      40.5 

Total  copper  slagged,%  52 .  \ 
Hatio  of  PbO  to  the 

copper  in  the  ore ...  69 : 


3.09     3.09     2.92 
51.64  50.3     47.3     51.1     50.3 
33.5     27.7     26.6     49.4     48.6 


26.2     26.7 
3.09  3.09 
50.4     51.2 
51        52-5 


29:1 


46:1 


Ore 

.  .  .       IO 

IO 

IO 

IO 

IO 

i  A.T. 

IO 

IO 

Bicarb  soi 

ia    " 

.       IO 

IO 

IO 

IO 

•7Q 

I  e 

IO 

10 

Borax 

<( 

IO 

Litharge 

« 

.     I  IO 

I^O 

I  ^O 

I  IO 

I  IO 

I  IO 

I  IO 

IIO 

Nitre 

a 

14. 

Id 

Id 

Id 

Id 

2d 

Id 

Id 

Silica 

<e 

Q 

Salt.  . 

.   cover 

cover 

cover 

cover 

cover 

cover 

cover 

COV€ 

Time  of  fusion,  min. 


Temperature,  degrees  C. 
Color  of  salt 


25 


910     1130     1040     1400     1320     1140 


low  15  high  15 
high  10  low  10 

730     1380 
1400       730 
—         —         —       pink     white     —         — 

Weight  of  lead 30.9     27.7     31.5     31.3     37.7     11.9     29.4       29.5 

Gold  ounces 3.12  not  determined  2 .98       not  deter'd 

Silver     "       50.5 

Total  copper  slagged,  %       45.9 

Ratio  of  PbO  to  the  cop-  v . '     ' •- 

per  in  the  ore 46:1          63:1  46: 


36.6     55.4     36.3     41.5 


47-8 
52.9     43-5 


45-7 


31:1 


46:  i 


The  per  cent  of  copper  in  the  total  slag  and  salt  varied  from 
.6%  to  1.15%. 

Fusions  15  and  16,  32  and  33,  35  and  36  show  that  the 
temperature  has  very  little  effect  on  the  amount  of  copper 
slagged. 


122  NOTES  ON  ASSAYING. 

Borax  and  soda  evidently  do  not  aid  it:  fusions  39  and  40. 
Fusion  40  shows  the  effect  that  the  increase  of  soda  has  upon 
the  size  of  the  lead  button. 

Silica  seems  to  help  it:  fusion  44.  A  very  high  ratio  of  PbO 
to  ore  or  to  the  copper  present  in  the  ore  certainly  helps  the 
slagging  of  the  copper. 

A  small-sized  lead  button,  provided  it  collects  the  precious 
metals,  seems  advisable. 

Silver  in  Antimonial  Ores. — On  an  ore  (R.P.  =  o)  containing 
antimoniate  of  lead  (antimony  25  per  cent  and  lead  40  per  cent) 
the  following  charge  gave  results  fully  as  satisfactory  as  the 
scorification  method.  F  crucible  was  used. 

Ore iA.T. 

Bicarbonate  of  soda 40  grammes 

Borax  glass 15 

Litharge 70 

Argols(R.P.  =  8) si       " 

Cover  of  salt. 

Here,  as  in  the  case  of  copper  ores,  high  litharge  was  used 
hi  order  to  oxidize  the  antimony  and  either  slag  it  or  volatilize  it. 

The  lead  buttons  were  soft  and  malleable  and  cupelled  sat- 
isfactorily. 

If  the  litharge  is  not  high,  the  antimony  will  go  into  the  lead 
button,  which  when  cupelled  will  give  trouble.  If  the  anti- 
mony is  present  in  large  amount,  the  cupel  will  be  cracked  all 
to  pieces;  if  in  smaller  amount,  the  edges  of  the  cupel  will  be 
bulged  out,  cracked,  and  a  scoria  left  on  the  inner  surface. 

The  following  ore  (roasted  stibnite)  will  serve  as  an  example. 

Gangue  quartz  and  slate;  antimony,  as  oxide,  i47/4o%. 

A.  B. 

Ore i  A.T.  10  grammes 

Bicarb,  of  soda 30  grammes  10 

Borax 10  10         " 

Litharge 60         "  90 

Argols 2j       "  2i       " 

Silica 2  2 

Cover  of  salt.  Cover  of  salt. 


ASSAY  OF  ORES  FOR  SILVER.  123 

In  A  the  cupel  was  coated  with  scoria  and  was  partly  cracked. 
The  edges  were  mvch  bulge  i  and  very  rough. 

In  B  the  cupel  was  free  from  scoria  and  showed  no  signs  of 
cracking. 

Concentrates,    mainly    Sb2S3   with    some    gangue.     R.P.  =4. 

Concentrates i  A.T. 

Bicarbonate  of  soda 15  grammes 

Borax 10 

Litharge 90 

Nitre 8 

Silica 3 

Cover  of  salt. 

Pyrrhotite. — This  ore  or  its  presence  in  another,  unless  it 
is  roasted  and  then  assayed,  generally  gives  trouble,  for  it  is  a 
difficult  one  to  decompose.  All  the  precautions,  previously 
laid  down  for  assaying  sulphide  ores,  should  be  carefully  observed, 
otherwise  the  final  fusion  will  be  unsatisfactory,  the  slag  full 
of  lead  shot,  and  the  size  of  the  lead  button  uncertain. 

High  soda  and  a  high  temperature  are  necessary,  especially 
in  finding  the  reducing-power,  otherwise  the  value  will  be  too 
low,  causing  subsequent  trouble  in  the  regular  fusion.  The 
following  results  were  obtained  upon  a  pure  pyrrhotite: 

PRELIMINARY  FUSIONS. 

Ore,  grammes         222222 

Bicarb,  of  soda,         "               4              4              4  2  8  8 

Litharge,                     "              60             60             60  80  60  60 

Cover  of  salt  in  each  case. 

Temperature High          Low         High  High  High  Low 

Lead,  grammes 18.01       15-96       17.46  15.66  17.81  17.06 

R.P 9               7-98         8-73  7-83  8.9  8.53 

INFLUENCE  OF  BICARBONATE  OF  SODA  AND  BORAX. 

Pyrrhotite,            grammes /...  12  12                      12 

Bicarb,  of  soda,         "       30  48  None 

Borax,                         ' '       None  None                  20 

Time  of  fusion,  minutes 35  35  35 

Fusion Very  liquid     Very  liquid              * 

*  Took  a  long  time,  and  the  result  was  some  slag  and  a  matte  (FeS),  weighing. 
10  grammes. 


124 


NOTES  ON  ASSAYING, 


Regular  Fusion. — Here  the  amount  of  bicarbonate  of  soda 
must  be  large  whether  the  iron  method  is  used  or  some  other, 
and  the  fusion  must  be  a  long  one.  Except  in  the  iron  method, 
the  litharge  must  be  high,  i.e.  fully  15  to  20  per  cent  in  excess 
-of  the  amount  called  for.  Borax  seems  to  be  of  no  advantage, 
and  little  if  any  need  be  used  except  in  the  fusion  with  iron. 
'Silica  is  necessary. 

No.  of  fusion,  .  .  . 

Ore,A.T.(R.P.  =  9 

Bicarb,  soda,  grms. 

Borax, 

Litharge, 

Nitre, 

-Silica,  ' ' 

Nails  (20-penny) .          5 


I 

i 

2 

I 

4 

1 

6 

i 

7 

8 

40 

40 

40 

15 

15 

40 

40 

40 

20 



20 

20 

20 

20 

— 

— 

3° 

70 

70 

130 

15° 

150 

150 

150 

one 

27 

27 

27 

27 

27 

27 

27 

4 

3 

3 

3 

3 

-3 

3 

7 

Cover  of  salt  in  each  case. 


Time,  minutes.  .  .        50 
Matte..  .  .    None 


40 
Small 


45 
None 


Lead. 
Slag. 


40          35  35 

Small     None  Slight 

amount  amount  coating 
27           9.8         12.6       38  36  25 

Very     Full  of   Full  of  Full  of  Good     Clean 

lead        lead        lead  and         and 

shot        shot        shot  liquid     liquid 


40 
None 


28 
Clean 


40 
None 


29 
Fusion 


liquid 
and 
good 


Crucibles  very 
little  attacked 


and    very  fine 
liquid  and  slag 


clean 


Fusions  i  and  8  were  the  most  satisfactory. 

All  the  fusions  show  the  necessity  of  high  soda  with  this  ore, 
and  fusions  No.  2  and  3  show  clearly  that  the  litharge  cannot 
be  cut  down,  as  is  the  case  with  many  ores,  even  when  the  soda 
is  high  and  a  large  amount  of  nitre  is  present.  If  silica  is  not 
present  in  the  ore  the  addition  of  from  40  to  50  per  cent,  to 
form  an  iron  silicate,  is  recommended. 

Ores  Carrying  Barite. — Fluorspar,  as  well  as  fluxes  acting  as 
acids  like  silica  and  borax,  is  very  helpful  in  decomposing  these 
ores. 

The  following  fusions  were  made  on  an  ore  carrying  zinc 
blende  and  chalcopyrite  in  a  gangue  having  a  high  percentage 
of  BaSO4  in  it.  The  R.P.  of  the  ore  was  4. 


ASSAY  OF  ORES  FOR  SILVER. 


1 

I 

15 

IS 

75 
8 

v5 
3° 

75 
8 

25 

75 
8 

* 

3° 

15 

75 
8 

'  soda,  gram 

mes        15 

10 

75 
8 

Ore,  A.T 

Bicarb,  o: 

Borax, 

Fluorspar, 

Litharge, 

Nitre, 

Silica, 


Time  of  fusion,  minutes.  . . 
Lead,  grammes. 
Lead  and  matte,  ' '  . 
Slag 


3  —          — 


Cover  of  salt  in  each  case. 
30  3° 

7-2 


40 
26 


Very 
liquid 


3° 
27 

-         16.3 
Good        — 


I25 

- 

6 

7 

$ 

i 

3° 

IS 

15 

— 

10 

10 

15 

5 

— 

75 

75 

90 

8 

8 

8 

— 

5 

8 

40 

3° 

3° 

27 

20 

24 

A  little 
thick 

Very 
fine 

Very 
fine 

fusion 

fusion 

and  slag 

Fusions  3  and  4  again  show  the  absolute  necessity  of  the. 
presence  of  soda  in  the  fusion  of  a  sulphide  ore. 

Fusions  6  and  7  were  the  most  satisfactory. 

In  all  the  crucible  work  which  has  just  been  described  the 
student  has  not  only  weighed  the  ore  out  accurately,  but  the 
fluxes,  the  object  being  to  make  him  familiar  with  the  chief 
assay  reagents,  to  show  him  why  they  are  used,  why  certain 
amounts  are  taken,  and  what  influence  the  reagents  have  upon 
each  other.  If  he  understands  their  action  and  the  theory  of 
their  use,  then  he  should  be  able  to  assay  any  ore.  If  he  does, 
not  understand  them,  then  it  becomes  a  mere  matter  of  guess- 
work. 

Now  in  the  regular  work  of  a  busy  laboratory  it  is  impossible 
to  weigh  out  each  reagent,  so  there  is  always  a  general  flux  mix- 
ture kept  on  hand  and  a  certain  measured  amount  is  taken,  pro- 
portional to  the  weight  of  ore  used.  The  ore  of  course  is , 
weighed  out  accurately,  the  general  flux  taken  by  measure  and. 
anything  else  added,  which,  from  its  character,  the  assayer  judges 
the  ore  requires. 

One  flux  mixture  has  been  given  on  page  113.  Another,  used 
in  a  Western  laboratory,  consists  of: 

3.07  kilos,  of  K2CO3, 
2.7        "      "    Na2C03, 
2-55      "       "    borax  glass, 

.45      "       "    flour, 
13.6        "      "    litharge. 


126  NOTES  ON  ASSAYING. 

Another  mixture  consists  of 

9  kilos,  of  litharge, 

9     "      "  borax, 

ii  to  13     "      "  bicarbonate  of  soda, 
113  grammes  charcoal. 

It  will  be  noticed  in  these  mixtures  that  flour  is  used  as  a 
reducing  agent  in  place  of  argols,  which  are  given  in  these  notes. 
One  may  not  be  able  to  obtain  argols,  but  one  can  always  obtain 
•either  charcoal,  flour,  starch,  or  something  which  will  act  as  a 
reducing  agent  and  answer  just  as  well  to  throw  down  a  lead 
button.  Any  one  studying  assaying  in  a  well-equipped  labora- 
tory is  expected  to  learn  the  reasons  for  the  different  steps  in  his 
work;  after  leaving  one  must  adapt  himself  to  his  surroundings 
and  the  conditions  he  finds,  which  he  can  easily  do  if  he  has  a 
;good  fundamental  knowledge.  If  he  lacks  this  knowledge  and 
:simply  works  by  rule  of  thumb  and  uses  a  flux  mixture  which 
lie  has  found  to  work  successfully  on  some  simple  ore  from  a  cer- 
tain district,  he  will  surely  be  in  trouble  when  he  meets  with  some 
difficult  ore  from  elsewhere. 

All  silver  in  an  ore  above  one  ounce  is  paid  for,  the  price 
teing  95%  of  the  New  York  quotation  for  silver  at  the  time  of 
sale  of  the  ore. 


CHAPTER    IV. 
ASSAY  OF   ORES   FOR  GOLD. 

GOLD  fuses  at  1064°  C.    Sp.  gr.  =  19.3.   Atomic  weight  =  197.2* 

The  first  thing  one  should  bear  in  mind  in  assaying  ores  for 
gold  is  that,  even  in  a  fair-grade  ore,  we  are  working  upon  material 
which  is  carrying  an  extremely  low  percentage  of  the  metal.  An 
ore  carrying  J  oz.  of  gold  per  ton  of  2000  Ibs.  av.,  or  .0005  gramme 
to  the  A.T.,  is  a  good  ore,  and  many  ores  carrying  only  .2  oz. 
($4TL.s_)  to  the  ton,  or  .0002  grammes  to  the  A.T.  are  worked  at  a 
profit. 

With  such  a  small  amount  to  weigh  and  base  our  results 
upon,  the  student  can  easily  see: 

i  st.  That  he  must  be  perfectly  exact  in  all  his  work. 

2d.  That,  as  a  rule,  the  amount  of  ore  taken  should  be  larger 
than  we  use  in  the  assay  of  ores  for  silver  or  lead. 

3d.  That,  in  order  to  obtain  satisfactory  results,  it  is  necessary 
to  have  the  sample  pulverized  extremely  fine.  That  is,  the  ore 
should  pass  a  i2o-mesh  sieve  at  least,  and  in  many  cases  a  i  Co- 
mesh  or  2oo-mesh  sieve  is  none  too  fine. 

Any  of  the  ores  the  student  has  previously  assayed  for  silver 
may  also  contain  gold. 

As  a  rule,  gold  occurs  chiefly  in  veins  of  quartz,  but  it  is  also 
found  in  slate,  granite,  gneiss,-  and  syenite. 

One  saying  is,  "gold  is  found  wherever  you  find  it,"  and 
Cripple  Creek  seems  to  illustrate  this.  It  occurs  both  native 
and  associated  with  sulphides.  Pyrite  and  arsenopyrite  are 
most  frequently  met  with,  but  any  sulphides,  such  as  galena, 
chalcopyrite,  and  blende,  may  be  auriferous.  Above  the  water 
level  most  veins  are  heavily  stained  with  iron  oxide,  due  to  the 

127 


128  NOTES  ON  ASSAYING. 

weathering  of  pyrite,  arsenopyrite,  or  any  sulphide  carrying  iron. 
The  following  are  very  rich  gold-bearing  minerals: 

f  Te  60%  approximately.. 
Sylvanite  (graphic  tellurium),  sp.  gr.  7.99  to  8.3  )  Au  30% 

(  Ag  10% 

C  Te  58% 
Calaverite  (telluride  of  gold),  sp.  gr.  9.04 <  Au  39% 

*Ag    3% 
Petzite  (telluride  of  silver  and  gold),  sp.  gr.  =8.7  to  9.2 

Ag  40%  to  50%;  Au  24%  to  25%,  the  remainder  tellurium. 
Foliated  tellurium  carries  Au,  Pb,  Te,  S,  and  Sb. 

In  making  the  assay  we  have  the  following  steps : 

i  st.  Collection  of  the  gold  and  silver  in  the  ore  by  means  of 
lead  in  the  scorification  process,  and  by  means  of  litharge,  reduced 
to  lead,  in  the  crucible  process.  The  gangue  and  the  impurities, 
in  the  ore  pass  into  the  slag. 

2d.  Cupellation  of  the  resulting  lead  button. 

3d.  Weighing  the  Au+ Ag  bead,  if  the  Ag  is  to  be  determined. 

4th.  Inquartation  of  the  bead  if  found  necessary. 

5th.  Parting  the  button  in  HNO3  or  H2SO4,  washing  with 
H2O,  and  transferring  the  gold  to  an  annealing-cup  or  por- 
celain crucible. 

6th.  Drying,  heating,  and  weighing  the  gold. 

Gold  ores  may  be  divided  into: 

Class  I.  Ores  with  no  sulphides,  arsenides,  or  material  of  a 
reducing  nature  in  the  gangue. 

Class  II.  Ores  with  sulphides,  arsenides,  etc.,  in  the  gangue, 
or  ores  with  a  reducing  power. 

Class  III.    Telluride  ores. 

METHODS   THAT   MAY   BE    USED    FOR   ASSAYING. 

Class  I.  (Scorification  Method.)  A.  Do  not  use  this  method 
unless  it  is  necessary  as,  for  instance,  in  the  case  of  copper  ingots 
or  bars  and  material  rich  in  copper,  zinc  residues  jrom  the  KCy 
process  and  similar  material  not  suitable  for  the  crucible  assay, 
fhe  loss  of  gold  is  greater  in  scorifying  than  in  cupelling.  If 
obliged  to  use  this  method,  take  TV  A.T.  of  the  substance  and 
proceed  as  described  under  the  Assay  of  Copper  Matte  and  Zinc 


ASSAY  OF  ORES  FOR  GOLD. 

Residues  for  Gold.  If  the  ore  is  poor,  it  may  be  necessary  to 
take  six  or  more  portions.  Finally  combine  these  and  base  the 
result  in  gold  upon  the  total  substance  taken. 

Some  assayers  use  4"  to  5"  scorifiers,  take  J  A.T.  of  ore,  a. 
large  amount  of  PbO,  borax  glass  and  some  reducing  agent,  and 
fuse.  This  is  not  strictly  a  scorification,  but  rather  a  fusion  or 
melt  in  a  scorifier,  and  there  is  often  difficulty  in  obtaining  a 
lead  button  of  the  proper  size. 

Class  I.  (Crucible  Method.)  B.  This  may  be  done  either 
in  a  pot-furnace  or  in  a  muffle.  It  has  the  great  advantage 
over  the  scorification  in  that  a  much  larger  quantity  of  ore  can. 
be  used,  i.e.,  i  A.T.  or  more. 

As  in  the  assay  of  ores  for  silver,  the  active  fluxes  are  two. 
or  more  times  the  amount  of  the  ore  taken. 

Use  G  or  H  crucibles  and  fuse  in  a  pot-furnace,  as  described 
in  the  assay  of  ores  for  silver. 

The  following  will  serve  as  illustrations  of  charges  to  be  used 
on  ores  of  different  character. 


No.  i.          No.  2. 
Silicious    Limeston 
Ore. 

No.  3.            No.  4.             No.  5. 
e.  Ore  contain-  Hematite.       Roasted 
ing  Fe2O3                           Concentrates^ 
either                                  Oxidizing 
native  or                               power  =  f-- 
due  to 
roasting  FeSa.                          (a)           (6> 
i                    i                    *             i 

40                            30                            30                  20 

20      bor.  gl.  8     borax  10            10 
30                  70                  30          100 
7*                   3                      2*            4 
4                       7t                    3               7"t- 
f  salt        cover  of  salt              cover  of  salt 
25                  16*         30 

H 

Lead 

Ore   A.T. 

(a) 
i 

i 
30 
5 
60 
t* 

salt 

i 
40 
15-25 
3° 

2* 

5 
cover  o 

Bicarb,  soda, 
Borax, 
Litharge, 
Argols  (R.  P.  = 
Silica  (SiO2), 

button,  gms. 

gms.  60 
5 
"      3° 
10),"        2* 

cover  of 

No.  6.  N 


Ore  carrying  43%  Cr2O3. 
1 2%  Copper.  (a)  (b)  (c) 

f  Ore *  A.T.  Ore i  A.T.       i  A.T.        i  A.T. 

J3   v      Bicarb. soda,        gms.        15  Bicarb,  soda,  gm.      60  60  30 

Borax,  10  .*      Borax,  "        20 

PbO,  "  90-110  S      Litharge,  "        35  35  70 

Argols  (R.P.  =  i  o),  gm.       2$  Argols,  '**.....    3  3  3 

SiO2,  "          3  Glass,  "        15       SiO2i5   Glass   20 

Cover  of  salt  Cover  of  salt  in  each  case 

A  large  amount  of  argols  cannot  Time,  minutes  ....    45  35  35 

be  used,  for  copper  will  be  reduced,  Lead,  grammes.  ...    26  29 

therefore  it  is  always  advisable  to  70  and  76  fused  well. 

determine  the  oxidizing    power  of  70  gave  a  slag  full  of  lead  shot ;  slag  too  basic, 

the  ore  so  as  to  obtain  about  a  20-  Slags  and  crucibles  yellow,  due  to  chromates 

gramme  lead  button.  of  lead  and  soda. 

*  Or  sufficient  to  reduce  the  Pb.    (See  pages  73,  89,  and  go.)  t  See  pages  75  and  76. 


NOTES  ON  ASSAYING. 

If  more  than  i  A.T.  of  ore  is  taken,  increase  the  fluxes  some- 
what. Do  not  change  the  litharge  where  30  grammes  are  used, 
and  take  only  sufficient  reducing  agent  to  give  a  lead  button  of 
the  desired  size.  Personally  I  do  not  believe  in  using  more  than 
i  A.T.  of  ore  in  a  G  or  H  crucible  because  sufficient  fluxes  can- 
not be  added  to  decompose  the  ore  without  the  charge  boiling 
over,  yet  I  know  that  some  assayers  use  as  high  as  4  A.T. 

If  an  ore  contains  copper  running  not  over  25%,  assay  it  for 
gold  as  described  in  the  Assay  of  Ores  for  Silver,  Special 
Methods.  That  is,  take  only  \  A.T.  of  ore  in  place  of  i  A.T., 
use  high  litharge  and  silica  in  order  to  slag  the  copper,  and  an 
amount  of  reducing  agent  sufficient  to  just  bring  down  a  lead 
button  of  the  desired  size.  Keep  the  active  fluxes  two  or  more 
times  the  ore,  as  described  under  assay  of  ores  for  silver. 

Fusion  in  the  Muffle. — This  is  conducted  as  described  under 
the  Assay  of  Ores  for  Silver.     Use  an  A  or  B  crucible. 
The  charge  is  made  up  on  the  following  lines :        Fe2O  . 

Ore 1  A.T.  JATV 

Bicarb,  soda 15-10  grammes          15 

Borax  glass 0-5  10 

Litharge 60-90  70 

Argols(R.P.  =  io) -2}        "  3i 

Glass 10 

or 

Silica 1-3       "  8 

Cover  of  salt. 

If  an  ore  is  so  poor  or  low  grade  that  an  unweighable  amount 
of  gold  is  obtained  from  i  A.T.,  then  I  think  it  advisable  to  pro- 
ceed as  follows: 

Very  Low  Grade  Ores  or  Tailings. — Ores  of  this  character 
can  be  assayed  by  either  of  the  following  methods: 

1.  Take  5,  10,  or  more  portions  of  i  A.T.  each,  fuse  in  G 
or  H  crucibles,  add  silver  to  each  lead  button,  cupel  separately, 
and  part  all  the  silver  and  gold  beads  in  one  flask. 

2.  Take  5  A.T.  of  ore  and  fuse  in  a  K  or  L  crucible  with 
the  following  fluxes: 


ASSAY   OF  ORES  FOR  G(JLL>.  131 

Bicarbonate  of  soda 150  grammes 

Borax 20  to  25        ' ' 

Litharge 300         ' ' 

Glass 20  to  25        '  * 

Argols  (R.P.=9) 10  to  12 

Cover  of  salt. 

The  actual  time  of  fusion  is  35  to  45  minutes,  but  owing 
to  the  size  of  the  crucible  and  the  amount  of  the  charge,  it  will 
take  i  hour  to  ij  hours  from  the  time  the  crucible  is  placed  in 
the  furnace  until  the  charge  is  poured. 

The  button  of  lead  (90  to  120  grammes)  may  be  scorified 
once  in  a  3^"  scorifier  by  pouring  off  the  slag,  and  the  resulting 
lead  button  cupelled  with  silver,  or  it  may  be  cut  into  four  pieces, 
silver  added  to  each  and  cupelled.  The  four  silver  and  gold 
beads  are  parted  in  one  flask.  When  a  small  amount  of  gold 
is  present,  the  loss  of  gold  is  practically  the  same  in  the  two  pro- 
cedures. 

Method  No.  i  gave  on  one   lot  of  tailings  .026  ounces  per  ton. 
No.  2    "      "   same"  "       "       .024      "        "     « 

Class  II.  (Crucible  Method.)  (Ores  with  sulphides,  arsen- 
ides, organic  matter,  or  material  of  any  kind  in  the  gangue,  with 
a  reducing  power.)  Use  G  or  H  crucibles. 

Method  C. — Scorify  and  treat  as  in  Class  I,  A — method  espe- 
cially adapted  to  copper  mattes. 

Method  D. — Roast  the  ore  and  then  treat  as  in  examples  3,  5, 
or  6,  Class  I,  B. 

Method  E.  (Method  with  Iron.  G  or  H  crucible.) — This 
requires  iron  in  excess,  a  large  amount  of  soda,  and  a  fixed 
•amount  of  PbO.  It  is  not  recommended  for  ores  containing  copper 
because  the  litharge  used  is  small;  nor  for  arsenic  and  antimony 
compounds,  for  a  speiss  may  be  obtained  unless  special  precautions 
are  taken 


132  NOTES  ON  ASSAYING, 

Ore i  A.T. 

Soda 60  grammes,  always  twice  the  ore. 

Borax 5-20      " 

Litharge 30         " 

Argols  i 

Iron      >  See  more  complete  description  of  the  process. 

Si02     ) 

Method  F.  (High  litharge.) — This  requires  a  large  quantity 
of  litharge  and  a  small  quantity  of  soda .  and  nitre  if  necessary. 
A  preliminary  fusion  must  be  made  to  determine  the  reducing; 
power  of  the  ore. 

The  method  is  especially  adapted  to  ores  containing  arsenic, 
antimony,  or  large  quantities  of  FeS2,  also  to  copper  ores,  when 
carrying  up  to  25  or  30  per  cent  of  that  metal.  Never  use  iron 
in  this  assay. 

Method  G.  (Fusion  in  the  muffle.)— Use  J  A.T.  of  ore  in 
an  A  or  B  crucible.  The  PbO  is  high,  the  soda  is  low,  the  borax 
glass  considerable,  and  nitre  is  used  if  found  necessary.  The 
object  is  to  have  a  fusible  slag  and  a  charge  that  will  not  boil  up 
much  in  the  crucible. 

The  following  description  will  give  a  more  complete  account 
of  the  foregoing  methods. 

Class  II,  C. — If  obliged  to  use  this  method,  see  Assay  of 
Copper  Matte  and  Zinc  Residues  for  Gold. 

Class  II,  D.  (Certain  ores  may  lose  considerable  gold 
under  this  method  of  procedure.) — The  method  of  roasting  ores 
containing  sulphur,  arsenic,  or  organic  matter  is  carried  out 
as  follows: 

Take  i  A.T.  or  more  of  ore,  place  it  in  a  clay  or  iron  dish 
made  for  roasting  purposes,  and  heat  the  ore  very  gradually  in 
a  muffle.  The  more  heavily  sulphuretted  the  ore  is  and  the 
more  fusible  the  sulphides  there  are  in  it,  such  as  PbS,  Sb2S3, 
and  Ag2S,  the  more  carefully  the  roasting  should  be  performed. 
Stir  the  ore  constantly  at  first,  to  prevent  its  caking.  //  it  does, 
cake,  throw  it  away  and  commence  again. 


ASSAY  OF  ORES  FOR  GOLD.  J33 

The  reaction  with  FeS2  is  as  follows: 


That  is,  we  desire  to  convert  the  sulphides  in  the  ore  into  oxides 
and  volatilize  the  S,  As,  and  Sb.  -Some  sulphates  and  arseniates 
will  also  be  formed.  Some  of  these  can  be  broken  up  by  heat 
alone  (2FeSO4-Fe2O3+SO2-fSO3  or  FeSO4  =  FeO+SO3  and 
2CuSO4  =  Cu2O+O  +  2SO3  or  CuSO4  =  CuO  +  SO2+O).  SO8 
breaks  up  into  SO2  and  O.  By  the  addition  of  carbon  we  can 
form  CO2,  SO2,  sulphide  of  carbon  and  the  sulphide  of  the  metal, 
which  will  then  break  up  and  decompose.  (2CuSO4+3C  =  Cu2S 
+  SO2-f  3CO2.)  Carbonate  of  ammonia  may  also  be  used, 
when  sulphate  of  ammonia  is  formed,  which  immediately  vola- 
tilizes. Towards  the  end  of  the  roast,  increase  the  heat  to  almost 
scorifying  temperature,  or  add  charcoal  until  no  SO2  can  be 
detected.  If  charcoal  is  to  be  used,  remove  the  dish  from  the 
muffle,  allow  the  ore  to  cool  slightly,  then  add  the  charcoal  and 
stir  it  in  well.  It  is  next  to  impossible  to  dead-roast  an  anti- 
monial  or  arsenical  ore,  and  if  arsenic  is  present,  the  odor  will  be 
noticed  at  this  time. 

Everything  in  the  ore  is  now  in  the  condition  of  oxide,  except 
the  gold  (which  is  in  a  metallic  condition),  and  some  lime  and 
lead,  which,  if  present  in  the  ore,  remain  as  sulphates.  Unless 
the  roasted  ore  contains  copper  or  other  metals  easily  reduced, 
assay  as  in  examples  3,  5,  or  6,  Class  I,  B. 

Class  II,  E.  (Iron  Method.  Pot-furnace.  See  also  page 
109  )  —  The  great  advantage  of  this  method  is  that  it  saves  making 
a  preliminary  fusion  and  finding  the  reducing  power  of  the  ore. 
The  student,  by  this  time,  ought  to  be  able  to  judge  fairly  well 
in  regard  to  the  ore,  its  composition,  how  to  make  up  a  charge, 
and  what  amount,  if  any,  of  argols,  iron,  and  silica  is  necessary.  For 
instance,  suppose  we  take  any  ore  to  be  assayed  and  van  it. 
What  we  obtain  on  the  vanning-shovel  will  depend  upon  the 
character  of  the  ore.  If  we  obtain  a  "fan"  like  that  shown  in 
the  cut  and  no  arsenical  or  cupriferous  minerals  are  present, 
the  charge  will  be  made  up  as  follows: 


NOTES  ON  ASSAYING. 


Sulphides 

(Slight  amount) 


Ore i  A.T. 

Bicarb,  soda,. ...  60  grammes 

Borax 5         " 

Litharge 40         " 

Argols(R.P.  =  io)     2 

Cover  of  salt. 
The  argols  will  reduce  20 
grammes  of  lead,  and  we  rely  on  the  ore  to  give  us  5  to  8  grammes 
more  lead,  still  leaving  some  PbO  in  excess.  No  iron  or  silica 
is  needed. 

If  the  ore,  upon  vanning,  shows  a 
"fan"  as  in  the  figure  annexed,  the  charge 
can  be  made  up  in  either  of  two  ways: 

Ore.  .  Aa?. . .    i  A.T.       Ore.  .  .  /.6? i  A.T. 

Bicarb,  soda  ....   30  gm. 

Borax 10  _  " 

PbO 60  "" 

Argols none 

Iron.. none 

SiO2 none 

Cover  of  salt 


Bicarb. soda.  60  gm. 

Borax 10  " 

PbO 30  " 

Argols none 

Iron i  nail 

SiO2 none 

Cover  of  salt 


In  a  the  ore  is  decomposed  by  both  the  iron  and  the  litharge 
and  we  have  a  lead  button  of  the  desired  size.     In  b  the  PbO 
decomposes  the  ore  and  in  so  doing  gives  the  lead  button. 

If  now  the  ore,  upon  vanning,  shows  a  "fan"  similar  to  the 
figure  below,  the  charge  is  made  up  as  follows: 

Ore...  ................         i  A.T. 

Bicarb,  soda  ...........       60  grammes 

Borax  ..................  10-20        " 

'  PbO  ..................       30 

Iron  nails  (twentypenny)  .         4 

SiO2.  ,  .................  .  3-5  grammes 

Cover  of  salt. 

(slight  amount)  .    Reactions  in  last  Fusion: 


FeS2  +  Fe  =  2FeS  ; 


PbO  +  Fe  =  FeO  +  t>b  ; 
FeO  +  SiO2  =  FeO,SiO2. 


> 

Some  iron  oxide  is  formed  by  the  oxidation  and  corrosion 
of  the  iron  nails  just  at  the  surface  of  the  fusion. 


ASSAY  OF  ORES  FOR   GOLD.  13$ 

The  FeO  goes  into  the  slag  or  combines  with  the  SiO2  from 
the  crucible  or  with  that  added. 

The  FeS  dissolves  in  the  highly  alkaline  slag,  and  the  SO2 
goes  off  as  a  gas  or  oxidizes  to  SO3  and  forms  Na2SO4. 

In  the  last  example  it  is  very  evident  that  30  grammes  of 
litharge  will  not  decompose  the  ore  taken,  so  a  large  amount  of 
iron  is  necessary  and  the  SiO2  is  added  to  combine  with  the 
FeO  formed  during  the  fusion,  which  would  otherwise  com- 
bine with  the  Si O 2  of  the  crucible  itself. 

The  amount  of  SiO2  added  depends  upon  the  amount  of 
sulphides  present  in  the  sample.  The  larger  the  amount  of 
sulphides  the  smaller  must  be  the  gangue  and  hence  the  amount 
of  SiO2  added,  to  combine  with  the  FeO  and  other  oxides  formed, 
must  be  large.  ' 

This  method  (E)  has  the  following  advantages: 

i st.  A  lead  button  of  the.  proper  size  can  be  obtained,  for 
the  quantity  of  litharge  used  is  small. 

2d.  The  crucible  charge  varies  only  slightly  with  different 
ores. 

The  disadvantages  are: 

r    i  st.  Th,e  difficulty  of  both  removing  the  iron  or  nails  from 
the  fusion  and  of  having  them  free  from  lead  globules, 

2d.  The  tendency  of  the  slag  to  be  rather  thick,  basic,  and 
corrosive. 

As  previously  stated,  for  i  A.T.  of  ore,  the  soda  is  60  grammes 
and  the  PbO  30  grammes,  unless  the  ore  carries  lead  when  less 
than  30  FbO  is  used.  The  borax  and  SiO2  must  be  increased,  as 
the  sulphides  in  the  ore  increase  and  as  the  gangue  becomes  basic. 

All  the  gold  must  be  extracted  from  the  ore,  and  in  order  to 
do  this  all  sulphides  present  in  the  ore  must  be  decomposed. 

Fusion.  (Gold  Ores,  Crucible  Method,  with  the  Use  of  Iron.) — 
The  fluxes  are  first  weighed  into  the  crucible,  and  the  ore  last  of 
all.  Mix  thoroughly,  hit  the  crucible  on  the  outside,  put  the 
nails  in  point  down,  and  then  cover  with  \"  of  salt.  Conduct 
the  assay  exactly  as  described  in  the  assay  of  a  silver  ore  by 
crucible  method  (pages  83  and  90).  After  the  ore  has  been  fused 
20  minutes  lift  out  the  nails  and  see  if  they  are  cutting  or  eating 
off  at  the  surface  of  the  slag;  if  so,  add  one  or  two  fresh  ones, 


I36  NOTES  ON  ASSAYING. 

leaving  the  others  in  the  crucible.  If  the  nails  cut  off,  it  is 
not  only  difficult  to  remove  them,  but  it  renders  a  satisfactory 
pour  impossible.  The  iron  present  in  the  slag  should  be  in  the 
condition  of  ferrous  oxide — ferric  oxide  tends  to  retain  gold  in 
the  slag.  Fuse  for  40  to  45  minutes  or  until  no  drops  of  lead 
are  seen  adhering  to  the  nails,  when  they  are  raised  out  of  the 
fusion.  When  the  fusion  is  completed,  remove  them,  and  holding 
them  partly  in  the  fusion,  tap  them  gently  to  knock  off  any  adher- 
ing drops  of  metal.  Let  crucible  stay  in  the  furnace  two  or  three 
minutes  longer,  then  pour.  The  lead  button  is  cupelled  as  usual, 
but  it  may  not  start  to  drive  quite  as  quickly  as  other  buttons, 
owing  to  a  film  of  oxide  iron  that  is  present. 

Arsenical  Ores. — Students  are  advised  not  to  use  the  iron 
method  on  arsenical  ores  until  they  have  had  considerable  experi- 
ence, for  special  precautions  are  necessary. 

The  following  experiments  by  Mr.  G.  Barnaby,  1904,  will 
be  found  of  interest  in  this  connection. 

Arsenopyrite  is  a  very  common  mineral  in  Nova  Scotia  gold 
ores,  and  when  the  tailings  from  stamp-mills  are  concentrated 
the  concentrates  often  carry  a  high  percentage  of  arsenic,  30 
and  40  per  cent  being  not  uncommon.  The  following  is  the 
partial  analysis  of  gold  ore  No.  1462  A. 

Silica 3J-5o% 

Fe 20.61% 

Arsenic 20.53% 

Sulphur ii.  04% 

Reducing  Power,  3.6 

When  no  iron  was  used  in  the  fusion  the  following  results 
were  obtained : 

Weight  of  ore •&  A.T.  T%  A.T.  J  A.T.  -ft  A.T. 

Bicarb,  soda,  grammes 10  10  25  20 

Borax,                    "        10  —  — 

PbO,                      "        60  90  70  60 

Nitre,                     "         I  I  6  i 

:  Silica,                   "        3  2 

Iron,  "        

Cover  of  salt  in  each  fusion. 

'Time  fusion,  minutes 45  27  45  45 

Weight  of  Pb,  grammes 20.2  25.6  32.3  30 

"   "  Au,   "    00084  .00084  .00140  .00084 

Ounces  per  ton 2.8  2.8  2.8  2.8 


ASSAY  OF  ORES  FOR  GOLD. 


137 


j 


00  <j   O  «O  O   CO    •  >  w^3           .     .     .  o       vfl 

M  ^  \o       co      r>-  o  't  bo  £  «••  M  oo  O 

do 
f4                 S    S°g 

N 

•.              °    ;s.2 

co^OO         CO       <5   O   •*        w 

N      •    w   O      • 

CO         ON 

t^<j  0  »0  0  co    •  >  10  j2           •     •   "  S"  0  vO~  -t 

^           ll 

w  ^  co        to        No^bO^*^1"11"00     -r° 

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Ui         *°  ° 

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EH                      w.      J?S      coot-NvOv^-' 

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O  S       *c3-S  00             r-    •  co    •     •     • 

cow                 vQy        O^^             O-N... 

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cow                  toy        0        N        NOON... 

EH                                CO  (H         ^H 

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»        .                           Q;        nj        O  O\O  f-^  O         ... 
00<JO«OOCOO>>>0^           •     •     -OOOO     •     •     • 
^•vQ         co        •OQ'tW       \OCvwOO-'-- 

N<jco        to        J^>M^ 
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f"1                    r-  3      13       oio^tt^ot^i  f^^ 

p-3                   u     *"  ° 

1  oooi  * 

P^                   >oy       3       «WNOON^.M. 

to                                     ^_Q 

IIP  |.  jjiiilli! 

ijll^n: 

jlli: 

:  :H-             :      g-  •--;:: 

ET  "  : 

:  if      ?  I     &        1  ill 
•  :|         I    I          ^     .fcisl 

1:1      S  J§      !*r!la 

11il=  IB! 

No.  of  Fusion  
Ore  used  
Sodium  bicarbonate  gr 
Borax, 
Litharge, 
Silica. 
Iron  nails 
Salt  
Time  of  fusion,  minutes 
Temperature  

-L^aa.  grz 
Speiss 
Iron  consumed, 
Gold  in  Pb 
Ounces  gold  per  ton.  .  . 

v<  o>      w 

I  <U  10  co  t^TJ 

>  CO    •    w   ._, 

O  t    •   o 


cofe  lOOvOOO 
>   to    .  co    • 

8    S  "N 


IP. 

5   -o       -o 


i  O  in  O 

5   0>        to 


Sodium 
Borax 
Litharg 
Silica 
Nitre 


138  NOTES  ON  ASSAYING. 

A  second  sample,  1462  D,  consisting  of  concentrates  with 
a  R.P.  of  7.4  and  carrying  36.2  per  cent  arsenic  gave  the  follow- 
ing results.  Ore  through  100  sieve.  Assay  2.47  oz.  gold. 


No.  of  Fusion  
Ore  used  
Sodium  bicarb.,  gms.  .  . 
Borax,                      "  .  .  . 
Litharge,                  "... 
Silica,                       "... 
Ironnails(20penny),  gm. 
Salt  

40                 44                 48                    41 

.3A.T.    .3A.T.    .3A.T.    .3A.T. 

30                   60                120                   30 

5555 
3o            3o            30            30 

3333 
70.7         70.9         53.8         51.8 
cover       cover        cover          cover 

45 

.3A.T. 
60 

5 
3° 
3 
52.1 
cover 

49 

•  3A.T. 

120 

5 
3° 
3 
50-3 
cover 

Time  of  fusion,  minutes 
Temperature   deg  \ 

45             45             45             45 
usual       usual        usual          low 
1280         1235         1185           710 

45 
.low 
700 

45 
low 

575  C. 

TjCstd                 S^-^s.     .    • 

26  7         27.2         26  *         -26.8 

27.  < 

24.8 

Speiss, 

*.\j  .  y                  4.  i  ,  A 

13-33       n-44 

6.42             3.6l 

/     0 

1.04 

0 

22  .  6             24                   _ 

o 

o  .  6         10 

8.2 

7.  1 

Gold  in  lead,      "  

.  OO067        .  00069 

00070     .  00074 

.00072 

/ 

{not  deter- 

Ounces per  ton. 

2.23 

2-3 

2-33        2-47 

2  .40 

mined 

No  of  Fusion  

42 

46 

43 

47 

Ore  used    

.3A.T. 

.3A.T. 

.3A.T. 

.3A.T. 

.3A.T. 

Sodium  bicarb.,  gms.  .  . 

3° 

60 

3° 

60 

3° 

Borax,                     "... 

5 

5 

5 

5 

5 

Litharge,                 "... 

3° 

3° 

3° 

60 

3° 

Silica,                      "... 

3 

3 

3 

3 

3 

Iron  nails(20penny)  ,  gm. 

54-2 

53-4 

53-5 

55 

52 

Salt             

cover 

cover 

cover 

cover 

cover 

Time  of  fusion,  minutes 

45 

45 

45 

45 

10 

Temperature,  deg.  C.  j  „ 

.  25'  725    L. 

.  20'  I200H 

25'  735  H.  25'  1570  H. 
.  2o'-i235  L.  20'          L. 

25'  1400 
20' 

usual 

Lead                gms  

26.7 

26.9 

26.5 

26.7 

not 
weighed 

Speiss                  "  .    .    . 

7.83 

7.24 

14.58 

11.92 

3-3 

Iron  consumed 

19.  7 

26  7 

•2C  .  2 

2O.  2 



Gold  in  lead       "  

.00071 

*v*  /               —  j  -  — 
.00069           .00059 

y 

not  determined 

Ounces  t>er  ton.  . 

2.37 

2.7                     I.  06 

" 

The  conclusions  that  can  be  drawn  from  the  results  on  these 
two  samples  seem  to  be: 

i  st.  That  a  high  temperature  is  conducive  to  the  formation 
of  a  speiss. 

2d.  That  the  size  of  the  speiss  obtained  in  a  fusion  depends 


ASSAY   OF  ORES  FOR   GO  La  139 

upon  the  temperature  and  the  amount  of  alkali  (soda  or  potash) 
used  in  the  charge. 

3d.  That  at  a  high  temperature  the  speiss  begins  to  form  as 
goon  as  the  charge  fuses  (fusions  26  and  28). 

4th.  That  the  speiss  may  or  may  not  carry  gold. 

5th.  That  a  large  speiss  button  usually  carries  gold  and  the 
results  from  the  lead  alone  are  consequently  low. 

6th.  Both  too  high  and  too  low  a  temperature  should  be 
avoided.  The  latter  (fusions  u,  12,  and  13)  give  low  results, 
owing  to  incomplete  decomposition  of  the  ore. 

yth.  That  the  best  temperature,  at  first,  is  one  as  low  as  the 
fusion  can  be  conducted  and  yet  have  the  ore  decomposed,  finish- 
ing with  high  (fusions  14,  15,  16,  and  35).     Fusions  made  in  this 
way  give  either  no  speiss  or  so  small  a  one  that  the  gold  contents, 
will  not  be  appreciable. 

8th.  That  as  the  alkali  flux  increases  the  iron  consumed  at  a, 
given  temperature  diminishes,  due  no  doubt  to  the  formation  of 
arseniate  and  arsenite  of  soda,  both  of  which  are  found  in  the  slag,, 
rather  than  to  the  formation  of  arsenide  of  iron. 

If  ores,  carrying  as  high  a  percentage  of  arsenic  as  these,  can 
be  assayed  by  this  method  and  no  speiss  result,  it  would  seem  as 
though  the.  method  could  be  satisfactorily  used  where  only  a 
small  percentage  of  arsenic  was  present,  simply  by  increasing 
the  alkaline  flux  and  maintaining  the  correct  temperature. 

Iron  Method.  Fusion  in  the  Muffle. — Ores  in  this  class  may 
be  fused  in  the  muffle  also,  as  described  under  the  Assay  of  Silver 
Ores,  page  92,  using  J  A.T.  of  ore. 

Class  II,  F.  Large  excess  of  PbO  and  nitre  if  found  neces- 
sary. (See  also  Class  II,  Silver  Ores,  page  93.) — In  taking  up 
this  method  first  refer  to  and  consider  what  took  place  when  we 
found  the  reducing  power  of  charcoal  and  argols  (page  83),  and 
also  what  took  place  in  determining  the  reducing  power  of  silver 
ores,  pages  94  to  102.  Every  ore  containing  sulphides,  arsenides, 
etc.,  or  with  a  reducing  power,  should  have  this  reducing  power 
determined  in  the  same  manner  by  a  trial  or  preliminary  fusion. 

Proceed  as  in  Class  II,  pages  103  to  100.  ruse  for  10  LO  20 
minutes  or  until  fusion  is  quiet.  Pour  and  weigh  the  resulting 


140  NOTES  ON  ASSAYING. 

lead  button  and  calculate  the  reducing  power  of  the  ore.  Sup- 
pose 2  grammes  of  the  ore  gave  14.8  grammes  of  lead,  then  the 
R.P.  =  7.4. 

Keeping  in  mind  that  litharge  (PbO)  and  nitre  (KNO3)  are 
both  strong  oxidizing  agents  and  that  they  are  both  able  to  decom- 
pose sulphides  and  similar  compounds,  it  follows  that,  having 
found  the  working  reducing  power  of  any  ore,  we  can  make  up  a 
charge,  as  we  did  in  the  assay  of  ores  for  silver,  to  obtain  a  result- 
ing lead  button  of  any  size  we  wish.  This  lead  button  should 
carry  all  the  silver  and  gold  in  the  ore.  Ores  to  be  treated  by 
this  method  may  be  divided  into  three  subclasses,  based  upon  the 
quantity  of  reducing  material,  i.e.,  sulphides,,  arsenides,  etc., 
present  in  the  sample. 

a.  Ores  requiring  a  reducing  agent  in  the  regular  fusion. 

b.  "  "        no       "  "      "     "         "  " 

c.  "  "        an  oxidizing  "      "     " 

i  A .  T.  of  ore  is  used  in  the  regular  fusion  unless  it  contains 
much  copper  or  has  a  reducing  power  of  4^  or  over,  when  only 
\A.T.  is  taken. 

The  following  will  serve  as  examples: 

No.  i  a.  No.  26.  No.  $c.  No.  40. 

Suppose  the  preliminary  fusion  on..      10  5  3  2  grammes  ore 

gave  a  lead  button  of 3  5  12  14.8  grammes. 

Then  the  working  R.P.  = 3  i  4  7-4 

Make  up  the  charges  for  the  regular  fusion  as  follows,  using 
G  or  H  crucibles  in  pot-furnace : 

No.  4*. 

IA.T. 

15 
10 
130 

19 

30 

5 


No.  i  a. 

No.  2&. 

No.  3<:. 

X 

y 

Ore 

I  A.T. 

i  A.T. 

i  A.T.   or  i 

A.T. 

Sodium  bicarb,  grms  

30  or  60 

30  or  60 

3° 

60 

Borax, 

5        5 

IO         IO 

IO 

10 

litharge, 

"       ... 

60      45 

75       50 

140 

90 

Argols  (R.P.  = 

=  9),    "       ... 

2            2 

—      — 

— 

— 

Nitre  (O.P.= 

4.2),"       ... 



—      — 

21 

21 

Glass, 

" 

— 

5        5 

25 



or  SIC* 

" 

— 

—      — 

6 



Cover  of  salt 

in  each  case. 

ASSAY  OF  ORES  FOR  GOLD. 


141 


We  aim  to  obtain  a  lead  button  weighing  between  26  and  30 


grammes. 

No.  i a. 

We  require  some  reduc- 
ing agent  in  this  fusion, 
because  i  A.T.  of  ore 
will  reduce  only  8.7 
grammes  of  lead. 
Therefore  we  add 
enough  argols  to  re- 
duce 1 8  more  grammes 
of  lead. 


No.  26. 

There  is  sufficient  reduc- 
ing material  in  this 
ore  to  give  a  zg-gm. 
lead  button.  There- 
fore we  require  neither 
argols  (reducing  agent) 
nor  nitre  (oxidizing 
agent). 


No.  3c. 

In  charge  x  the  ore  will 
reduce  29.166  X  4  = 
116.6  grammes  of 
lead.  We  desire  a 
26-gramme  button. 
.*.  116.6  —  26  =  90.6 
grammes  of  lead  to 
be  oxidized. 

Oxidizing  power  of  nitre 

90.6 

=  4.2  .  - — =21    gm. 
4-2 

of  nitre  to  be  added. 


No.  36.  In  charge  y,  the  30  additional  grammes  of  soda 
take  the  place  of  the  50  grammes  of  PbO  left  off.  Owing  to 
this  diminution  of  litharge  no  silica  is  used,  otherwise  the  charge 
is  the  same  as  x. 

No.  4C.  Here  \  A.T.  of  ore  is  used,  but  the  charge  is  made 
up  on  the  same  basis  as  No.  y  x;  the  amount  of  litharge  in  each 
case  is  20  per  cent  in  excess  of  the  total  amount  of  lead  that  each 
ore  will  reduce,  i.e.,  ore  No.  y  oc  will  reduce  29.16X4=116.6 
grammes;  20  per  cent  of  this  is  23,  or  a  total  of  140  grammes. 

This  is  lead,  but  it  is  sufficiently  close  to  call  it  litharge  with- 
out figuring  the  exact  amount  of  litharge  that  will  yield  140 
grammes  of  lead. 

Summing  up  this  method,  the  first  thing  necessary  is  to 
determine  the  working  reducing  power  oj  the  ore  and  then  the 
oxidizing  power  of  the  nitre,  after  which  calculate  the  total 
amount  of  lead  that  the  ore  intended  to  be  used  in  the  regular 
fusion  will  reduce;  if  less  than  30  grammes,  add  sufficient 
argols  to  make  up  the  difference;  if  it  will  reduce  more  than 
30  grammes,  subtract  25  to  30  from  the  amount  reduced,  not  from 
the  PbO  used,  and  divide  the  difference  by  the  oxidizing  power  of 
the  nitre;  this  will  give  the  amount  of  nitre  necessary  to  add  to 
the  regular  fusion. 

Regular  Fusion. — The  fusion  is  made  in  the  pot-furnace  in 
the  usual  manner.  When  the  charge  begins  to  fuse,  check  the 


142  NOTES  ON  ASSAYING. 

fire  AT  ONCE,  to  have  the  charge  fuse  quietly.  The  more  nitre 
there  is  present  the  greater  the  care  to  be  observed,  because  the  action 
at  times  is  very  violent.  The  nitre  and  PbO  both  decompose 
vthe  sulphides  present,  and  the  nitre  no  doubt  oxidizes  some  of 
the  lead  reduced,  when  it  is  in  small  globules,  but  in  what  order, 
if  any,  these  reactions  take  place  it  is  difficult  to  say. 

Most  ores  will  be  decomposed  by  a  fusion  of  25  to  30  minutes, 
but  for.  heavily  sulphuretted  ores  50  minutes  is  sometimes  neces- 
sary. 

The  disadvantages  of  the  process  are: 

i st.  The  necessity  for  a  preliminary  fusion. 

2d.  The  liability  of  an  excess  of  PbO  eating  through  the 
crucibles. 

3d.  The  possibility  of  obtaining  a  button  differing  in  weight 
from  that  figured  for. 

The  last  two  can  be  avoided,  if  due  care  is  given  to  the  work 
and  ij  the  same  ratio  of  soda  to  ore  is  maintained  in  the  regular 
fusion  as  was  used  in  the  preliminary  one.  An  excess  of  soda 
(as  shown  under  Silver  Assay,  page  97  and  following)  seems 
to  tend  to  form  SO3  rather  than  SO2,  and  consequently  the  amount 
of  lead  obtained  is  greater  when  a  large  excess  of  alkali  is  used. 
This  method  is  especially  adapted  to  arsenical,  antimonial, 
and  copper  ores.  The  first  two  are  oxidized  and  either  volatilized 
-or  slagged,  and  the  last  is  slagged  by  the  excess  of  litharge  used. 
The  lead  button,  if  soft  and  malleable,  is  cupelled  as  usual. 

Class  II,  F.  (Fusion  in  the  Muffle.) — Ores  in  this  class  can 
be  fused  in  the  muffle,  as  described  under  the  Assay  of  Ores  for 
Silver.  For  instance,  the  charge  for  ore  3^  on  page  140  would 
be  made  up  as  follows.  Use  a  B  crucible. 

Ore........ i  A.T. 

Sodium  bicarbonate 10  grammes 

Borax  glass 10 

Litharge 90 

Nitre  (O.P.  =4.2) 7  " 

Glass 5 

Cover  of  salt. 


ASSAY  OF  ORES  FOR   GOLD.  143 

The  fusion  would  have  to  be  made  very  carefully  owing  to 
the  nitre  present. 

Fuse  40  to  50  minutes. 

Class  III.  Telluride  Ores. — Ores  carrying  tellurium  com- 
pounds are  certainly  more  difficult  to  assay  for  gold  than  the 
ordinary  run  of  ores,  and  when  there  is  a  large  percentage  of 
tellurium  present  satisfactory  results  are  extremely  difficult  to 
obtain.  At  one  time  the  scorincation  method  was  supposed 
to  be  the  only  satisfactory  one,  but  equally  uniform  results  can 
be  obtained  by  the  crucible  method,  if  all  due  precautions  are 
taken  and  the  ore  is  sufficiently  fine  (170- to  2oo-mesh).  In  the 
former  a  large  amount  of  lead  and  a  high  temperature  are  essen- 
tial, and  in  the  latter  a  high  temperature  and  a  large  amount  of 
alkali.  The  idea  is  to  have  the  tellurium  form  a  tellurate  of 
soda  and  enter  the  slag  or  else  be  oxidized  by  the  litharge.  Some- 
times one  button,  among  several  assays  conducted  under  con- 
ditions as  near  alike  as  possible,  carries  much  more  tellurium 
than  the  others,  and  results  on  some  rich  ores  lead  me  to  believe 
that,  in  these  instances,  the  tellurium  compounds  which  have 
entered  the  slag  are  broken  up  and  the  tellurium  enters  the  lead 
button.  Much  gold  can  be  lost  when  roasting  ores  rich  in  both 
gold  and  tellurium.  Low-grade  ores,  when  little  tellurium  is 
present,  can  be  roasted  with  little  loss  of  gold,  and  assays  on  these 
roasted  ores  will  always  run  much  more  uniformly  than  upon  the 
raw  ores.  It  will  be  seen  from  these  preliminary  remarks  that 
there  is  room  for  much  valuable  investigation  upon  this  class  of 
ores. 

Numerous  papers  have  been  published  in  regard  to  the  cor- 
rect method  of  assaying  these  ores,  and  many  different  charges 
and  methods  have  been  suggested.  No  doubt  they  all  have 
their  advocates,  and  in  their  hands  satisfactory  results  may  be 
obtained.  The  thing  more  important  than  all  others  is  to  see 
that  the  ore  has  been  ground  to  a  sufficient  degree  of  fineness. 
For  the  majority  of  rich  ores  this  is  not  less  than  what  will  pass 
through  a  lyo-mesh  sieve,  or  finer  if  possible.  In  other  words, 
the  richer  the  ore  the  finer  the  sieve  should  be  through  which 
it  should  be  passed. 

The  following  experiments  were  carried  out  by  Mr.  A.  L. 


144 


NOTES  ON  ASSAYING. 


Davis  of  the  class  of  1898,  and  were  first  published  in  the  Tech- 
nology Quarterly,  Vol.  XII,  No.  2,  June  1899: 

"The  ore  selected  for  the  work  came  from  Boulder  County, 
Colorado,  and  gave  a  strong  test  for  tellurium.  The  per- 
centage was  not  determined.  The  gangue  was  chiefly  quartz, 
with  tellurides  and  pyrite  scattered  through  it.  It  was  pul- 
verized and  passed  through  a  ico-mesh  sieve.  Assays  made 
by  myself  showed  68.6  ounces  gold  by  the  scorification  method, 
and  68.3  ounces  gold  by  the  crucible  method  of  assay,  no  cor- 
rection being  made  for  gold  left  in  slag  and  cupel.  The  ore 
had  a  reducing  power  of  1.2. 

"  In  the  experiments  carried  out  by  Mr.  Davis  four  different 
crucible  charges  were  tried,  and  three  different  scorification 
charges.  In  each  experiment  the  slags  and  cupels  were  saved, 
ground  separately  and  assayed,  in  order  to  trace  the  loss  of  gold, 
if  there  was  any.  The  results  are  shown  in  the  accompanying 
tables.  From  the  tables  it  will  be  seen  that,  in  the  scorification 
process,  some  gold  is  always  lost  in  the  slag,  and  that  it  is  larger 
than  the  loss  sustained  in  cupellation,  which  of  course  is  the 
rule  in  gold  assays.  In  the  crucible  process  there  is  also  a  loss 


SCORIFICATION    METHOD. 


g 

.1      * 

€ 

£ 

-0 

4^ 

1 

i 

•5  •£ 

•g    8 

rt 

a.  . 

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bo 
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1 

I. 

It 

Charges. 

I 

1 

8  " 

&      <*> 

*l 

•o  S 

•fc 

.a 

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M 

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O 

I 

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9 

O 

O  o 

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Pn 

{Ore  j'a  A  T.  . 

lb 

30 
30 

20        

cupelled 

.00622 
.00648 

.00005 

.00004 

.00631 

63.1 
64.8 

•  79 

•63 

Gran,  lead,  60  gms. 

(£  mixed  with  ore, 

£  placed  on  top). 
Borax  glass,  a  pinch  on 

3C 

31 

cupelled 

.00690 

trace 

trace 

.00690 

69 

.00 

.00 

top  of  all. 

fOre  T^  A.T.  .    .. 

ie 

34 

22       

.00686 

.  00004 

none 

.  00690 

69 

.58 

none 

Gran,  lead,  45  gms. 

II.    •{      ($-    mixed    with 

ore)  

2f 

25 

cupelled 

.00648 

.  00005 

.  00005 

.00658 

65.8 

.•76 

.76 

{  PbO  cover  10  gms. 

3S 

25 

cupelled 

.00650 

.00010 

.00006 

.00666 

66.6  i  .50 

.90 

Borax  glass,  0.3  gms.  on 

top  of  all. 

(  Ore  rV  A.T  

ih 

2J 

48 
49 

37      20 
25     — 

.00684 

.  00647 

.00005 
trace 

none 
.  00005 

.00689 
.00652 

68.9 
65.2 

.00 

none 
•  77 

III.    •{  Gran,  lead,  60  gms. 
|  PbO  i  A.T. 

Assays  a,  e,  and  h  were  all  made  at  the  same  time  and  under  conditions  as  nearly  alike 
as  possible. 

Assays  b,  f,  and  /  were  all  made  at  the  same  time  and  under  like  conditions. 


ASSAY  OF  ORES  FOR  GOLD. 


145 


of  gold  in  the  slag,  but  the  percentage  loss  seems  to  be  less  than 
that  sustained  in  cupellation. 

"  As  the  ore  carried  very  little  silver,  enough  pure  silver  was 
added  to  all  the  lead  buttons  at  the  time  of  cupellation  to  part 
the  resultant  bead.  It  may  be  of  interest  to  state  that  tests  upon 
the  bone- ash  from  which  the  cupels  were  made  by  us  showed 
that 

3.5%  would  remain  on  a  6o-mesh  sieve. 

15.9%  would  pass  60  and  remain  on  80. 

27.8%  would  pass  80  and  remain  on  100. 

52.8%  would  pass  through  loo-mesh  sieve. 

CRUCIBLE    METHOD. 


4 

d 

bo 

I 

1 

.S 

i 

-d 

•a 

1 

L 

Charges. 

Experime 

] 

•a 

1 

1   . 

1 

:  Gold  Obt; 
rrammes. 

i 

•d 

3 

1 
'o 

I 

1 
1 

Cent  of  Tota 
jund  in  Slag. 

Cent  9f  Tota 
5und  in  Cupe 

o 

% 

rt  o 

rt'^ 

•30 

oj 

o  & 

. 

'5 

-4  o 

+JH 

-4->    S 

-(jQ 

•^VM 

w-fo 

«-•£« 

£ 

£ 

£ 

£~ 

| 

| 

£__ 

0 

1 

1 

I. 

[Ore  i  A.T. 
.£  j  Soda,  60  grammes.  . 

i 

30 





.03391 

.00007 

.00008 

.03406 

68.12 

.  21 

.23 

Si  PbO,  120 

^Argols,  i  gramme..  . 
Borax  glass  cover. 

2 

27 

— 

— 

.03417 

.00019 

lost 

.03436 

68.72 

.56 

— 

II. 

fOre  *  A.T. 

...  |  Soda,  20  grammes.  . 

I 

80 

47 

21 

.03463 

none 

none 

•03463 

69.26 

none 

none 

S  \  PbO,   80           " 

s  i  Gran.  Pb,  50  " 

2 

75 

5i 

25 

.03387 

.00008 

.00012 

.03407 

68.14 

.24 

•  35 

(.Argols,  i  gramme... 

Cover  of  salt. 

III. 

f  Ore,  i  A.T. 

v,  |  Soda,  40  grammes.  . 

I 

29 

— 



•03393 

trace 

.00008 

.03401 

68.02 

—^- 

.24 

a  i  PbO,  60 
^  1  Borax  glass,  15  gms. 

2 

25 

— 



.03414 

.00005 

.00014 

•03433 

68.66 

•  IS 

.41 

(.Argols,  r  gramme..  . 
Cover  of  salt. 

3 

25 

~ 

.03401 

trace 

.00016 

.03417 

68.34 

.46 

IV. 

{Ore,  i  A.T. 

Soda,  60  grammes.  . 
Borax  glass,  15  gms. 
PbO,  60  grammes..  . 

I 
2 

25 
28 

.06698 
.06820 

.00009 

.00011 

.00005 
.00015 

.06712 
.06846 

67.12 
68.46 

•  13 
.16 

.07 

.22 

Cover  of  salt. 

Av. 

68.32 

Taking  all  the  results  between  68  and  69  oz.  we  have  an  average  of  68.35  oz. 

"  From  the  foregoing  tables  it  is  very  evident  that  the  ore, 
setting  aside  the  loss  through  volatilization,  assays  between  68 
and  69  ounces  per  ton,  and  any  results  below  this  are  due  to 


146  NOTES  ON  ASSAYING. 

the  ore  weighed  out  not  being  a  correct  or  even  sample  of  the 
whole.  Of  the  eight  scorification  assays  three  are  practically 
correct,  and  are  within  the  limits  of  error  of  assay,  with  no  cor- 
rection made  for  the  gold  found  in  the  slag  and  cupel.  The 
remaining  five  are  all  too  low,  even  with  the  corrections  made, 
and  there  seems  no  way  for  accounting  for  these  low  results 
other  than  that  the  portion  of  ore  taken  was  an  incorrect  sample 
of  the  whole. 

"  The  crucible  results  are  much  more  even,  and  the  percentage 
of  loss  sustained  both  in  the  slag  and  in  cupellation  lower  than 
in  the  scorification  method.  As  the  amount  of  ore  taken  is 
five  times  larger  in  seven  cases  and  ten  times  larger  in  two  cases 
than  in  the  scorification  method,  this  may  account  for  the  more 
uniform  results  and  the  smaller  percentage  of  loss  sustained. 

"  As  for  the  charges  used,  no  comparison  is  drawn.  Our  only 
regret  is  that  the  sample  of  ore  was  so  small  that  we  were  unable 
to  carry  out  further  experiments  which  the  above  results  sug- 
gest. No  doubt  if  the  ore  had  been  crushed  to  pass  through  a 
1 60-  or  i8o-mesh  sieve  more  uniform  results  would  have  been 
obtained  in  the  scorification  method.  It  was  only  a  short  time 
^ago  when  a  6o-mesh  sieve  was  considered  sufficiently  fine  to 
pass  any  ore  through  previous  to  assaying.  This  was  then  set 
aside  for  an  8o-mesh,  and  now  a  loo-mesh  is  generally  used 
in  most  assay  offices.  I  believe  it  only  a  question  of  time  when 
every  sample  will  have  to  pass  a  i4o-mesh.  What  assayers 
need  is  a  machine  easily  cleaned,  which  will  grind  ores  through 
such  a  sieve  quickly,  and  at  the  same  time  not  contaminate  the 
sample  with  the  iron  or  material  of  which  the  machine  is  made. 
The  foregoing  experiments  also  bring  up  the  questions  of  how 
close  assay  results  should  check,  and  what  the  percentage  of  loss 
is  in  assay  work. 

"  As  to  the  first  question,  some  ores  will  check  easily,  even  if 
the  ore  is  ground  no  finer  than  through  a  6o-mesh  sieve,  but 
these  are  the  exceptions.  With  other  ores,  even  when  ground 
;so  fine  that  they  will  pass  through  bolting- cloth  finer  than  200 
meshes  to  the  inch,  it  seems  impossible  to  obtain  anything  like 
uniform  results. 


ASSAY  OF  ORES  FOR   GOLD.  147 

"As  to  the  percentage  of  loss  sustained  in  work,  whether  by 
the  scorification  or  the  crucible  method,  many  experiments 
carried  out  upon  the  foregoing  lines,  both  upon  silver  and  gold 
ores,  indicate  to  me  that  nothing  definite  can  be  laid  down  in 
regard  to  it.  Every  ore,  every  slag,  every  scorification,  and 
every  cupel,  let  alone  the  temperature  at  which  the  assay  is 
carried  on,  has  some  effect  upon  the  loss,  and  these  make  too 
many  unknown  quantities  to  arrive  at  any  definite  conclusion." 

The  following  additional  data  were  obtained  by  Mr.  C.  E. 
Danforth,  class  of  1905. 

Two  ores  used,  both  through  lyo-sieve,  analyzed  as  follows: 

No.  i.  SiO2  =  78.5%;    Te  =  5.i6%;    FeS2,  CaO,  and  H3PO4 
also  present.     R.P.^- 

Gold,  wet  analysis  ....................  287.7  oz- 

"      scorification  assay  ..............  287.02  " 

11  crucible  assay  .................  287.9  " 

Silver  ...............................  258.3    " 


No.  3.  Si02  =  74-5%;  Te  =  7.i%;  FeS2,  CaO,  and  H3PO4 
also  present.  Gold  256.4  oz.  Silver  826  oz. 

At  the  time  of  cupellation  C.P.  silver  was  added  to  each  assay 
to  diminish  the  loss  of  gold  absorbed  by  the  cupel.  This  amount 
added  to  that  present  in  the  ore  made  the  ratio  of  silver  to  gold 
6  to  i. 

Different  temperatures  and  many  variations  in  the  fluxes  were 
experimented  with.  The  dry  and  wet  methods  of  analysis  for 
gold  were  also  compared. 

The  results  of  this  work  seem  to  show  : 

i  st.  That  uniform  results  are  very  difficult  to  obtain  by  any 
method  on  ores  as  rich  in  gold  and  carrying  as  much  tellurium 
as  these  two  do. 

2d.  That  the  ore  should  be  weighed  on  balances  sensitive  at 
least  to  .02  of  a  milligramme. 

3d.  That  when  ores  carry  as  much  tellurium  as  these  do,  i.e., 
when  a  little  ore  gives  a  strong  pink  solution  with  H2SC>4,  no  more 
than  ^V  A.T.  of  ore  should  be  used  for  any  fire  assay,  otherwise  tel- 


148  NOTES  ON  ASSAYING. 

lurium  will  be  present  in  the  resulting  silver  and  gold  bead,  giving 
it  a  rough  and  frosted  appearance. 

4th.  That  in  scorification  work  a  large  amount  of  lead  and  a 
high  temperature  (1000°  C.  or  more)  are  necessary. 

5th.  That  the  addition  of  PbO  in  scorification  helps  to  elim- 
inate the  tellurium,  but  the  silver  and  gold  results  are  both  low. 

6th.  That  in  crucible  work  a  large  or  small  amount  of  litharge 
may  be  used.  A  high  temperature  seems  advisable  and  especially 
high  soda,  but  if  the  ratio  of  soda  to  both  ore  and  litharge  is 
very  high  (soda  30  grammes,  litharge  25,  ore  ^V  A.T.),  the  tem- 
perature may  be  low. 

The  ratio  of  bicarbonate  of  soda  to  ore  varied  from  3.4  to  i 
up  to  20  to  i;  the  ratio  of  litharge  to  ore  from  17  to  i  up  to  31 
to  i,  and  the  ratio  of  soda  to  litharge  from  i-J-  to  i  up  to  i  to  9. 

The  temperature  varied  from  890°  to  1240°  C. 

yth.  That  the  addition  of  nitre  does  not  prevent  the  tellurium 
from  passing  into  the  lead  button. 

8th.  That  the  presence  of  tellurium  in  a  silver  and  gold  bead 
aids  the  parting  in  H^SCU.  The  parting  is  more  rapid  and  the  gold 
is  left  in  one  piece  in  a  spongy  condition.  This  spongy  appear- 
ance seems  to  be  a  very  delicate  test  for  tellurium,  for  in  all 
cases  where  the  H^SO*  was  colored  pink  the  gold  was  spongy, 
and  in  many  instances,  when  a  very  slight  amount  -of  tellurium 
was  present,  it  was  spongy  when  the  H2SO4  showed  no  trace  of 
color. 

A  third  ore,  carrying  only  a  small  amount  of  tellurium,  gave 
no  trouble,  the  results  being  very  uniform.  It  would  all  pass 
through  a  2OO-mesh  screen,  had  a  R.P.  of  .7,  and  assayed  2.60  oz. 
gold  and  11.46  oz.  silver. 

The  following  are  some  charges  which  have  been  given  to 
me: 

Mr.  G.  A.  Packard,  class  of  1890,  for  rich  ores  in  San  Juan 
district,  Colorado,  recommends  a  crucible  assay  with  ^  A.T.  of 
ore,  litharge  60  grammes,  some  soda,  some  potash,  the  necessary 
amount  of  reducing  agent,  and  a  cover  of  borax  glass. 

Mr.  C.  S.  Hurter,  1898,  recommends  a  crucible  assay  with 


ASSAY  OF  ORES  FOR  GOLD.  149 

}  A.T.  of  ore  and  not  less  than  180  to  200  grammes  of  litharge, 
increasing  the  amount  of  the  acid  fluxes  owing  to  the  large  amount 
of  litharge. 

Mr.  J.  H.  Batcheller,  1900,  recommends  the  following: 

i  A.T.  if  the  ore  is  rich. 

i  A.T.  "     "      "    "  poor. 

(Soda 40  parts  "\ 
Potash 20     " 
Flour  8     "       I        X  W 

Borax 10     "     J 

50    "     PbO. 
5     "     silica. 

Cover  with  30  grammes  of  borax  glass.  - 
Heat  at  just  as  high  a  temperature  as  the  muffle  will  give. 
In  Cripple  Creek,  Colo.,  they  take  -fa  to  £  A.T.  of  ore,  i\ 
oz.  of  a  flux  made  up  somewhat  as  follows,  and  fuse  in  a  muffle- 
furnace.     The  slag  will  be  glassy  and  brittle. 

Flux.  Ore  J  A.T. 

K2CO. 3 . 07  kilos  ^  c§         f  IO    grammes 

Na,C03 2.70     "  Q 

Borax  glass 2.55      " 

Flour 45     " 

Litharge 13 . 60     " 

68.3  grammes  or 
about  2^  oz. 

Testing  an  Ore  for  Tellurium. — Take  some  of  the  finely 
pulverized  ore  and  heat  gently  with  strong  H2SC>4  in  a  white 
vessel.  If  tellurium  is  present,  a  faint  purple  tinge  will  be  seen 
about  the  ore  particles  which  will  gradually  spread  through  the 
solution,  coloring  it  deep  carmine  if  much  is  present.  The  cause 
of  this  color  is  doubtful;  some  say  it  is  due  to  tellurous  oxide, 
others  to  tellurium  sulphite.  It  will  disappear  on  boiling  and 
upon  the  addition  of  water,  which  throws  down  the  metal  as 
a  grayish-black  powder  (TeSO3+H2O  =  Te  +  H2SO4).  If  the 
ore  itself  gives  no  test,  take  100  grammes  or  more  of  the  ore 
and  carefully  pan  it;  then  treat  the  concentrates  as  described. 


150  NOTES  ON  ASSAYING. 

The  following  are  some  references  as  to  telluride  ores: 
C.  W.  Fulton,  School  of  Mines  Quarterly,  Vol.  XIX. 
Mineral  Industry,  Vol.  VI,  Telluride  Ores. 
Effect  of  Tellurium  upon  the  Cupellation  of  Gold. — The  fol- 
lowing work  was  done  by  Messrs.  F  . J.  Eager  and  W.  W.  Welch : 


No. 

C.P.  Gold. 

Lead, 

Grammes. 

Temp. 
C. 

Percentage 
of  Tellu- 
rium Used. 

Percentage 
Gold  Lost. 

Mean 
of  the 
Two. 

I 

.20181 

10 

775° 

none 

•15 

2 

.20104 

<  ( 

.16 

-155 

3 

.20025 

2-5 

.10 

4 

.  20408 

<  < 

.19 

-145 

5 

•  20334 

5.12 

.12 

6 

.  20089 

i  < 

.11 

.115 

7 

.  20392 

7-5 

•17 

8 

.  20590 

*  ' 

•15 

.160 

9 

.20226 

10 

.12 

10 

.  20263 

.16 

.140 

The  results  agree  very  closely  with  the  ones  obtained  when 
cupelling  pure  gold  (see  page  160)  and  seem  to  indicate  that  the 
presence  of  10%  of  tellurium  has  no  influence  on  the  loss  of 
gold,  which  is  entirely  at  variance  with  many  published  results*,, 
which  show  very  high  losses  when  tellurium  is  present  in  the 
lead  button.  All  the  buttons  were  bright  yellow  and  showed 
no  evidence  of  tellurium. 

The  tellurium  gave  a  pinkish  color  to  the  surface  of  the 
cupels,  which,  in  great  part,  faded  away  upon  cooling. 

Cupelling  and  Weighing  Beads  of  the  Precious  Metals. — If  the 
ore  is  to  be  assayed  for  both  silver  and  gold,  the  button  resulting 
from  the  cupellation  is  weighed  previous  to  the  parting  with  acid 
and  the  silver  determined  as  follows: 

Silver  and  gold  bead =  .  00847  grammes  in  i  A.T. 

Silver  in  30  grammes  of  PbO  used . . .  =  .00037 


Silver  and  gold =  .00810 

Gold  from  parting =  .00210 

Silver. .  .  .  =  .  00600 


=  2.1  oz. 
=  6  oz. 


ASSAY  OF  ORES  FOR   GOLD.  151 

There  is  sufficient  silver  in  this  button  for  parting;  but  if  a 
button  does  not  part  in  acid,  silver  has  to  be  added.  This  silver 
need  not  be  weighed.  The  final  calculation  is  made  as  in 
example. 

When  we  do  not  care  to  know  the  amount  of  silver  in  the 
ore  and  the  ore  is  known  to  carry  a  very  small  quantity  of  both 
silver  and  gold  or  a  large  quantity  of  gold  and  little  if  any  silver,. 
it  is  well  to  add  a  small  piece  of  C.P.  silver-foil  to  the  lead  but- 
ton at  the  time  of  cupellation.  This  will  not  only  give  a  button, 
but  will  allow  this  button  to  be  parted  and  save  fusing  it  with 
silver  afterwards.  Students  should  bear  in  mind,  however,, 
that  if  the  silver  is  in  too  great  excess  or  in  too  large  ratio  to  the 
gold,  the  button  is  apt  to  part  too  rapidly  and  the  gold  be  finely 
divided,  unless  very  weak  acid  is  used. 

Parting. — The  separation  of  gold  from  silver  is  called  "  part- 
ing." For  this  purpose  use  either  nitric  or  sulphuric  acid.  The 
acids  must  be  as  pure  as  they  can  possibly  be  made,  for  if  either 
one  contains  a  small  quantity  of  the  other,  gold  will  go  into  solu- 
tion. The  HNOs  must  also  be  free  from  HC1  and  free  chlorine. 
It  is  claimed  that  when  an  alloy  of  gold  and  silver  is  in  a  thin 
plate,  the  best  ratio  in  which  to  have  the  metals  is  between  2^- 
and  3  parts  silver  to  i  part  of  gold.  That  is,  an  alloy  of  this 
ratio  will  part,  leaving  no  silver  in  the  gold,  while  an  alloy  con- 
taining less  than  2^  parts  of  Ag  to  i  part  of  Au  will  not  part. 

My  experience  has  been  that  when  an  alloy  is  in  a  very  thin 
plate,  or  a  bead  is  small  and  has  the  ratio  of  silver  3  to  gold  i, 
it  may  part  and  leave  no  silver  or  an  extremely  small  amount 
in  the  gold,  but  in  the  ordinary  run  of  work  I  believe  it  is  advis- 
able to  have  the  ratio  from  6  to  10  of  silver  to  i  of  gold.  By 
having  this  ratio  the  button  is  sure  to  be  parted  and  results  in 
gold  too  high,  owing  to  the  presence  of  silver,  will  not  be  reported, 
which,  in  the  .case  of  beginners,  is  likely  to  occur  if  the  ratio  is 
3  silver  to  i  gold.  Furthermore,  many  recent  tests  seem  to  show 
that,  by  having  this  high  ratio  of  silver  present  during  cupella- 
tion, more  .correct  assays  are  obtained  for  gold  due  to  the  smaller 
absorption  of  gold  by  the  cupel. 


152  NOTES  ON  ASSAYING. 

The  danger  of  having  the  gold  finely  divided  during  the  part- 
ing, owing  to  the  high  ratio  of  silver,  can  be  easily  avoided  by 
using  very  dilute  acid  at  first. 

Mr.  T.  K.  Rose  *  recommends  dropping  the  flattened  beads 
into  boiling  nitric  acid  (sp.  gr.  1.25)  and  says  that  "under  these 
conditions  the  parting  is  rapid  and  complete  and  the  bead  hardly 
ever  breaks  up  whatever  its  composition.  Small  beads,  with 
much  silver,  part  almost  instantaneously,  large  beads  in  from 
five  to  ten  minutes,  and  no  second  acid  is  required." 

Inquartation  or  Quartation  (i.e.,  one  part  in  four). — This 
is  an  operation  by  which  the  alloy  or  button  is  brought  to  this 
standard  or  ratio. 

The  button  or  alloy  of  gold  and  silver  is  carefully  cleaned, 
weighed,  and  hammered  flat  on  a  small  anvil.  If  it  is  a  large 
button  or  bullion,  it  is  annealed  repeatedly  X~3  anc^  ro^ec^ 
out  gradually  into  a  thin  plate  or  ribbon.  '— ^  It  is  next 
rolled  up  into  the  form  of  a  cornet  or  of  a  coil  and  then  placed 
in  a  parting- flask.  In  parting  buttons  from  ores  some  assayers 
prefer  one  thing,  some  another;  small  flasks,  porcelain  crucibles, 
or  test-tubes  may  be  used. 

The  capacity  of  the  flasks  should  be  from  30  to  60  cc.,  and  the 
lip  should  be  round  and  not  liable  to  break.  The 
adjoining  figures  represent  two  forms  of  flasks.  B 
' A\  I B\  ^as  ^e  advantage  over  yl  in  that  the  sides  are 
straight,  and  they  both  have  the  advantage  over  a 
test-tube  in  that  the  contents,  when  heated,  are  not  so  apt  to 
bump.  In  France  and  in  some  mints  they  use  a  flask 
shaped  as  in  the  annexed  figure.  In  parting  we  do 
not  use  strong  HNO3  (1.42  sp.  gr.),  for  this  seems  to 
have  some  action  upon  gold.  (If  the  acid  in  which 
the  alloy  has  been  parted  turns  yellow  and  then  brown 
or  violet  upon  the  addition  of  water,  gold  has  un- 
doubtedly gone  into  solution.)  In  some  tests  .12  to  .15  per 
cent  of  gold  went  into  solution.  Acid  of  1.13,  1.16  (18°  Baume"), 
1.20,  and  1.27  sp.  gr.  may  be  used. 

*  Jl.  Chem.,  Met.  and  Mg.  Soc.  of  So.  Africa,  Jan.  1905. 


ASS  Ay   OF  ORES  FOR   GOLD. 


28° 
30.6° 
32-5° 

32-5° 


At  65°  Fah.                                            H2O. 

HNO3 
1.42  sp.  gi 

Acid  of 

.14    sp.  gr. 

s  made  up  of  700  cc. 

and    260  cc 

«      t( 

.18     "     " 

'      "      "   "  700  " 

"      38° 

It           ft 

.194  "     " 

'      "      "   "  700  " 

"      420 

time    " 

"      470 

«  <        <  i 

.25     "    "     '      "      "   "  700  " 

"      700 

900 

«        K 

.30     "    "   "      "      *'   "  700  " 

"      1  100 

' 

•  3l6  "    "  "      "      "  "  7°°  " 

1300 

Place  the  bead,  button,  or  strip  of  bullion  in  the  flask  or  porce- 
lain crucible,  add  a  little  distilled  water  and  then  just  enough 
acid  (1.20  sp.  gr.)  to  start  action  (the  mints  use  acid  of  three  dif- 
ferent strengths);  heat  gently,  the  object  being  to  have  the 
action  take  place  slowly,  and  finally  boil.  If,  after  boiling  a  few 
minutes,  no  action  is  noticed  upon  the  button  and  it  appears 
round  and  hard,  there  is  probably  not  sufficient  silver  present  in 
It.  Wash  with  distilled  H2O  and  transfer  to  an  annealing-cup, 
dry  and  weigh.  Add  more  than  three  times  the  weight  of  C.P. 
silver,  wrap  in  C.P.  lead,  and  cupel  on  a  fresh  cupel. 

If  upon  boiling  in  the  dilute  acid  there  is  action  upon  the 
button,  continue  the  boiling  until  action  almost  ceases,  decant 
the  solution  containing  the  silver  nitrate  (save  this  AgNO3  in  a 
bottle),  add  a  fresh  portion  of  acid  (1.20  sp.  gr.),  and  boil  again. 
Repeat  a  third  time  and  either  add  a  little  1.40  acid  to  the  1.20 
or  else  boil  in  1.27  sp.  gr.  acid  until  there  is  no  action  or  until 
the  last  traces  of  the  silver  are  removed  from  the  button  or  cor- 
net. The  acid  will  usually  boil  where  the  gold  particles  are; 
•do  not  mistake  this  for  the  solvent  action  of  the  acid  upon  the 
silver.  If  there  is  any  doubt  about  this  or  if  the  contents  of 
the  flask  are  inclined  to  bump,  place  a  light  stirring-rod  in  flask, 
when  the  boiling  will  take  place  chiefly  about  this.  If  the  student 
suspects  that  the  ratio  of  the  silver  to  the  gold  is  very  large,  have 
the  solution  of  the  silver  take  place  all  the  more  slowly,  so  as 
to  keep  the  gold  in  one  piece. 

The  boiling  tends  to  collect  the  particles  of  gold  and  removes 
any  air  from  the  fine  flakes.  Finally  rotate  the  flask  gently, 


154  NOTES  ON  ASSAYING. 

decant  the  solution,  and  wash  with  hot  distilled  water  two  or 
three  times.  When  decanting  the  solution  or  water  always  hold  a 
piece  of  white  paper  beneath  the  flzsk,  so  that  you  can  watch  the 
gold  residue. 

The  gold  is  then  ready  to  be  transferred  to  a  clay  or  porce- 
lain annealing-cup  or  to  a  porcelain  crucible.  The  clay  annealing- 
cups  or  dry  cups  should  have  round  smooth  edges  and  not  sharp 
ones.  The  Battersea  forms  A  and  B  cannot  be  improved  upon. 

The  clay  cups  have  the  advantage  over  the  glazed  porcelain 
ones  in  that  they  are  porous  and  can  absorb  some  water  and  give 
it  off  slowly.  They  have  the  disadvantage  that,  if  not  carefully 
used,  some  of  the  material  from  the  cup  or  cover  may  break  or 
rub  off  and  get  into  the  gold.  The  porcelain  cups  have  the  advan- 
tage of  the  surface  being  perfectly  smooth  and  glazed,  so  that  it 
cannot  be  rubbed  off  and  get  into  the  gold.  They  have  the 
disadvantage  of  breaking  more  easily  upon  heating  and  cooling 
and  of  being  apt  to  spatter  in  drying.  The  latter  can,  however, 
be  almost  entirely  obviated  in  the  following  way:  Have  only  a 
little  water  left  in  the  cup,  then  add  some  absolute  alcohol  and 
set  this  on  fire.  By  the  time  the  alcohol  has  all  burned,  the  water 
will  have  evaporated  and  the  gold  will  be  left  in  the  cup  in  a  con- 
dition to  stand  the  full  temperature  of  a  lamp  or  muffle.  When 
the  porcelain  crucibles  are  hot,  use  hot  tongs  with  which  to  handle 
them. 

The  next  step  in  the  parting  process,  if  a  flask  or  test-tube 
has  been  used,  is  to  fill  it  jull  to  the  edge  with  distilled  water, 
place  an  annealing-cup  or  porcelain  crucible  on  top,  and  invert 
quickly;  allow  the  gold  to  settle  into  the  cup,  shake  the  flask, 
tap  it  and  rotate  it  occasionally ;  raise  the 
flask  gently  and  allow  air  to  enter  slowly, 
but  do  not  allow  it  to  disturb  and  break 
up  the  gold.  When  the  mouth  of  the 
flask  is  even  with  the  top  of  the  cup  and 
the  latter  is  full  of  water,  slide  the  flask 
off  quickly  at  right  angles  to  the  cup, 

drain  the  water  from  the  cup  as  far  as  possible,  cover  it  up,  and 
dry  it  upon  an  iron  plate. 


ASSAY  OF  ORES  FOR  GOLD.  155 

The  gold  will  be  in  the  form  of  a  dark-brown  or  black  powder. 
Finally,  heat  the  cup  in  a  muffle-furnace  or  over  a  Bunsen  lamp 
until  it  is  red  on  the  bottom  and  the  gold  is  bright  yellow. 

During  the  whole  process  of  "parting"  the  student  must  be 
very  careful  to  get  no  foreign  matter  of  any  kind  into  the  flask  or 
the  annealing-cup.  Never  pass  one  flask  over  another  nor  one 
annealing- cup  over  another,  as  dirt  may  fall  off  one  into  the  other. 
If  the  student  heats  the  clay  annealing- cups  in  a  muffle,  which  is 
the  most  satisfactory  method,  have  them  dry  before  placing  them 

in   the  muffle   and  do  not  touch,  the 

__ 

^* —  muffle  or  furnace  in  any  way  during 
the  heating.  Handle  the  cups  care- 
fully with  tongs,  similar  to  those  represented  in  the  figure,  and 
keep  the  covers  on  them  until  ready  to  weigh  the  gold. 

When  the  cup  and  its  contents  are  perfectly  cold,  have  the 
fine  balances  (sensitive  to  YIOO  of  a  milligramme,  i.e.,  .00001 
gramme)  in  perfect  adjustment,  remove  the  scale-pan  from  the 
balances,  and  transfer  the  gold  from  the  cup  to  the  pan.  Do 
this  by  tapping  gently  the  side  of  the  annealing-cup.  This  should 
detach  any  small  particles  of  geld  which  may  be  adhering  there, 
and  then  by  tipping  the  cup  slowly  over  the  pan  all  the  gold  will 
slide  nicely  from  the  cup  into  the  pan.  Any  particles  adhering  to 
the  cup  may  be  detached  by  means  of  a  small  feather  trimmed  to 
a  fine  point.  Replace  the  scale-pan  and  weigh  as  accurately  as 
possible.  Report  the  result  in  ounces  cs  follows: 

Ore  used  =  i  A.T. 

Gold  as  weighed  =  .oo 1 26  grammes. 

=  1.26  oz.  per  ton  of  2000  Ibs.  of  ore. 
Value  @  $2o67/ioo  per  oz.   (U.  S.  Standard)  =$2604/100 

After  weighing  the  gold  always  examine  it  carefully  not  only 
to  see  whether  any  foreign  matter  has  been  weighed  with  it,  but 
also  to  see  whether  it  is  pure  yellow.  If  it  has  a  white  appearance, 
it  has  not  parted  and  contains  silver;  if  it  is  dark  or  black,  it 
probably  contains  some  of  the  rare  metals  of  the  Pt  group. 

Gold  cupelled  with  bismuth  almost  always  retains  traces  of 


156  NOTES  ON  ASSAYING. 

this  metal,  and  very  small  amounts  of  it  or  of  lead  may  make  the 
gold  brittle  and  non-malleable. 

The  "flashing"*  of  a  gold  button,  i.e.,  when  in  cooling  it 
.emits  a  brilliant,  clear,  greenish  light,  is  said  to  indicate  its  purity; 
and  if  this  takes  place,  Ir,  Rh,  Os,  Ru,  and  Oslr  must  be  absent, 
for  extremely  small  quantities  will  prevent  it. 

On  ordinary  ores  results  in  gold  should  agree  within  .02  oz. 
Assays  of  seller  and  buyer  should  check  within  .04  oz. 

If  the  seller  finds  1.42  oz.  and  the  buyer  1.38  oz.,  the  ore  is 
settled  for  at  1.40  oz.;  if  the  seller  finds  1.42  and  1.44  oz.  and 
the  buyer  1.35  and  1.36  oz.,  a  sample  of  the  ore  is  sent  to  an 
umpire,  who  makes  from  two  to  four  assays. 

Generally,  the  mean  of  these  assays  is  taken. 

Suppose  the  umpire  finds  1.40  oz.,  then  the  ore  is  bought  on 
that  basis. 

If  he  finds  1.46  oz.,  then  the  settlement  is  based  on  1.44  oz. 
If  he  finds  1.34  oz.,  then  1.36  oz.  per  ton  is  the  basis. 

Smelters  generally  pay  $19.50  to  $20  per  ounce  for  all  gold 
present  above  .05  of  an  ounce. 

*  Flashing  in  Assays  of  Gold.  Dr.  A.  D.  Van  Riemsdijk,  Chem.  News,  vol.  41, 
pp.  126  and  266. 


ASS  A  Y  OF  ORES  FOR   GOLD.  157 

Separation  of  Gold  from  Platinum  and  Iridium :   Wet  Method.* 

"The  method  consists  in  treating  the  solution  containing  the 
metals  with  10-15  cc-  °f  peroxide  of  hydrogen  after  the  addition 
of  about  5  cc.  of  an  alkaline  lye  (KHO  or  NaHO,  480  grammes  per 
litre).  While  other  methods  require  several  hours  tc  effect  a  com- 
plete reduction,  in  this  case  the  gold  is  precipitated  in  a  few- 
minutes,  even  in  the  cold,  as  a  black  deposit,  which  under  the 
action  of  heat  agglomerates  and  becomes  of  a  reddish-brown 
color: 

2AuCl3+  3H2O2+ 6KOH  =  2Au+ 6O  +  6KC1+  3H2O. 

In  case  of  dilute  solutions  it  is  best  to  apply  heat  after  the 
precipitation,  then  acidulate  with  HC1.  For  the  estimation  of 
gold  in  commercial  chloraurate  of  sodium  it  is,  however,  prefer- 
able to  effect  the  reduction  by  means  of  formic  aldehyde  instead 
of  hydrogen  peroxide. 

The  reaction  of  peroxide  of  hydrogen  in  alkaline  solution  is 
much  more  sensitive  qualitatively  than  any  other  reaction  of 
gold.  With  3  milligrammes  of  gold  per  litre  we  can  still  perceive 
a  pale  reddish  coloration,  appearing  blue  by  reflected  light;  this 
would  not  be  detected  by  other  reagents. 

Silver  is  also  precipitated  quantitatively  under  the  same  con- 
ditions, but  platinum  as  well  as  iridium  remains  in  solution; 
this  affords  an  excellent  method  for  separating  these  two  metals 
from  gold." 

EXPERIMENT:    ROASTING  CONCENTRATES  OR  AN   ORE  CARRY- 
ING GOLD. 

The  objects  of  the  test  are: 

i  st.  To  find  the  assay  and  value  of  the  concentrates  or  of  the 
ore. 

2d.  To  ascertain  the  loss  in  weight  of  concentrates  or  of  the 
ore  during  the  roast. 

3d.  To  assay  the  roasted  material  to  discover  the  loss  of  gold, 
if  any,  during  the  roast. 

4th.  To  see  how  good  an  assayer  one  is. 

*  Chem.  News,  vol.  82,  p.  70.  Estimate  of  gold  and  its  separation  from  Pt 
and  Ir.  L.  Vanino  and  L.  Seemann. 


IS8  NOTES  ON  ASSAYING. 

Take  the  concentrates  resulting  from  the  panning  test 
(through  30-  or  4O-sieve)  or  some  that  will  be  assigned  to  you. 
Mix  very  thoroughly  and  with  a  broad  spatula  take  a  sample  of 
200  grammes.  Roll  this  well  on  the  sampling  cloth  or  paper; 
take  with  a  broad  spatula  90  grammes  (weigh  on  flux- balance), 
crush  it  through  a  i2o-sieve  and  assay  for  gold.  Make  two 
assays,  using  i  A.T.  in  each  case,  unless  the  ore  carries  copper  or 
has  a  reducing  power  of  4^  or  more,  when  use  only  J  A.T.  Add 
silver  to  every  assay  unless  ore  is  known  to  carry  sufficient  silver 
jor  parting. 

Weigh  out  exactly  no  grammes  of  the  ore  (through  30-  or 
40-sieve)  on  the  pulp-balance  and  roast  carefully  in  a  clay  dish 
in  a  muffle  as  per  Class  II,  D,  page  132,  also  page  214. 

See  that  the  clay  dish  will  go  into  the  muffle  and  have  only 
sufficient  juel  in  the  furnace  to  come  up  to  the  bottom  oj  the 
muffle. 

Use  every  precaution  to  avoid  mechanical  loss  of  the  ore. 
Do  not  heat  so  fast  that  the  ore  will  decrepitate,  and  after  stirring 
the  ore  each  time  always  hit  the  ircn  stirring-rod  on  the  dish  to 
shake  off  any  ore  that  may  adhere  to  the  rod. 

Roast  the  ore  dead,  i.e.,  so  that  neither  sulphides,  sulphates, 
arsenides,  nor  arsenates  are  present  in  it. 

Weigh  the  roasted  ore  on  a  pulp-balance  to  the  second  place 
of  decimals,  and  calculate  the  per  cent  of  ore  lost  during  th: 
roast. 

This  loss  depends  entirely  upon  the  composition  cf  the  ere 
or  concentrates,  and  may  be  very  slight  or  as  much  as  40  per  cent. 

Grind  the  roasted  ore  through  i2O-sieve  and  assay  for  gold. 
(See  page  129,  examples  3,  5,  and  6.) 

As  the  ore  generally  loses  weight,  the  assay  of  the  roasted 
ore  must  necessarily  be  higher  than  that  of  the  raw  ore,  unless 
there  has  been  a  heavy  loss  in  gold. 

Report  as  follows: 

Example. — Concentrates  from  Ore  No.  2444.  Through  30- 
imesh  sieve.  Consist  of  arsenopyrite,  pyrite,  and  a  little  slate. 

Took  200  grammes  of  concentrates. 


ASSAY  OF  ORES  FOR   GOLD.  159 

Assay  showed  1.12  oz.  per  ton  of  2000  Ibs. 
Ore  taken  for  roasting  =  no  grammes 
Ore  after  roasting        =  86 

Loss  24        "       =2iT*V% 

Total  gold   in   no  grammes  =  29. 16 : 1 10 ::. 00112 :#=. 00422. 

Roasted  ore  assays  1.40  oz.  gold  per  ton. 

Total  gold  in  roasted  ore  is  29.16:86: :. 00140 :#=. 00413. 

Gold  lost  (.00422— .00413)  =  .00009  ==2-I3% 

The  foregoing  experiment  is  a  most  valuable  one  in  many  ways, 
for  it  shows  how  carefully  a  student  works,  how  good  an  assayer 
he  is,  and  how  much  he  has  profited  by  his  previous  work. 

Gold  volatilizes  easily  before  an  ordinary  blowpipe,  giving  a 
purple  stain  (oxide  of  gold);  to  prove  this,  hold  a  moist  vessel 
over  the  charcoal  or  cupel,  condense  the  fumes,  dry,  and  assay  the 
residue.  (See  Napier's  experiments.*) 

The  metal  in  the  mint,  when  in  crucibles  ready  to  pour  for 
coinage,  is  said  to  have  a  temperature  of  1100°  to  1150°  C. 
Metals  when  in  a  melted  condition  absorb  a  great  deal  of  gas,  and 
gold  is  no  exception.f  According  to  T.  K.  Rose,  an  atmosphere  of 
CO  apparently  increases  the  volatility,  and  he  says  that  the  loss 
in  clay  crucibles  is  less  than  in  cupels,  and  less  in  the  latter  than 
it  is  in  graphite  crucibles. 

The  following  results  and  those  given  on  page  150  are  of  interest 
in  this  connection. 

It  will  be  remembered  that  silver  can  be  cupelled  successfully 
at  700°  and  even  below,  but  this  cannot  be  done  in  the  case  of 
gold.  The  loss  in  gold  increases  gradually  with  the  temperature 
until  the  neighborhood  of  1000°  is  reached,  when  it  increases 
rapidly.  In  these  experiments  the  loss  at  this  temperature  was 
chiefly  due  to  minute  buttons  found  on  the  inner  surface  of  the 

*  Volatilization  of  Metallic  Gold.     Journal  of  Chem.  Soc.,  vol.  10,  p.  229,  by 
James  Napier.     T.  K.  Rose,  J.  of  Chem.  Soc.,  vol.  63,  p.  714. 
f  Phil.  Trans.,  1866,  399-439,  by  Graham. 


i6o 


NOTES   CN  ASSAYING. 


cupel.  At  first  it  was  thought  the  large  buttons  had  sprouted, 
although  they  presented  a  smooth  surface.  The  following  experi- 
ment was  then  tried:  Three  lots  of  gold  were  cupelled  side  by  side 
at  1000°  C. ;  one  was  withdrawn  when  the  10  grammes  of  lead  were 
about  half  cupelled,  another  when  nearly  at  the  point  of  blicking,. 
and  the  third  after  the  button  had  blicked.  All  the  cupels  had 
small  gold  buttons  scattered  over  them,  but  none  of  the  buttons. 
were  observed  to  spit.  On  the  one  first  withdrawn  the  gold 
buttons  were  small  and  few  in  number;  on  the  second  there 
were  more  buttons  and  larger  ones,  and  on  the  last  a  good  many 
quite  large  ones  were  found. 

CUPELLATION    OF    GOLD    AT    DIFFERENT    TEMPERATURES    TO 
DETERMINE  LOSSES. 

EXPERIMENTS  BY  MESSRS.  F.  J.  EAGER  AND  W.  W.  WELCH. 


No. 

Gold.     C.P. 

Lead, 
Grammes. 

Temp. 

(_/• 

Per  Cent 
Lost. 

Mean  of  the 
Two  Nearest 
Together. 

I 

.20026 

IO 

700° 

All  three  of 

these  buttons 

2 

.20176 

« 

froze   owing 

to  the  temper* 

3 

.20421 

M 

u 

ature  being 

too  low. 

4 

.20181 

I 

775° 

•15 

5 

.20104 

< 

.16 

.155 

7 

.20168 

< 

850° 

.40 

8 

.20047 

' 

•55 

9 

•20153 

< 

« 

•37 

.385 

10 

.20513 

c 

925° 

•45 

ii 

•20353 

« 

ii 

.46 

12 

.  20398 

( 

(t 

.46 

.460 

13 

.20180 

« 

1000° 

1.44 

14 

.20120 

M 

(1 

1.28 

IS 

.20166 

M 

(« 

i-43 

J-43S 

17 

.20251 

" 

1075° 

3-34 

18 

.20173 

«« 

2.64 

2.990 

Where  the  cupel  was  most  eaten  into  there  the  larger  number 
of  buttons  were  found,  and  the  softer  the  cupel  the  more  it  was 
eaten.  Hard  cupels  were  also  attacked,  and  where  eaten  there 
buttons  were  found,  which  seems  to  indicate  that  the  higher  the 
temperature  the  more  the  litharge  attacks  the  cupels,  for  no- 
small  buttons  were  found  on  the  same  quality  of  cupels  run 
below  icoo°  C.  At  high  temperatures,  for  some  reason  (perhaps 
less  capillary  attraction  of  the  lead),  small  particles  of  the  alloy 
are  left  behind  and  cupel  by  themselves;  therefore  gold  but- 


ASS  A  Y  OF  ORES  FOR   GOLD. 


i6r 


tons  should  not  be  cupelled  above  the  neighborhood  of  800°  C- 
It  was  noticed  in  these  tests,  as  in  the  case  of  the  cupellation  of 
silver  (page  63),  that  as  the  loss  of  gold  increased  the  color  of  the 
litharge  in  the  cupels  became  more  green.  To  determine  whether 
this  green  color  had  any  significance,  a  gold  button  weighing; 
1.4  grammes  was  cupelled  at  an  ordinary  temperature  and  the 
cupel  was  quite  green.  On  assaying  this  cupel  .00154  grammes, 
of  gold  were  recovered,  showing  a  loss  of  .11  per  cent  by  absorp- 
tion. 

The  following  are  other  examples : 


Gold  Button 
obtained. 


Gold  found 
in  Cupel. 

.00390  grammes 
.00462 


Per  Cent 
absorbed. 


3.2550  grammes 
3.2680 

The  following  table  shows  the  effect  of  copper  on  the  cupella- 
tion of  gold. 

Lead,  gold,  and  temperature  constant,  copper  varying. 


No. 

Gold 
C.P., 
Grammes. 

Lead, 
Grammes. 

Copper. 
Per  Cent  of 
the  Gold. 

Temp. 

Per 
Cent 
Loss. 

Mean  of 
the  Two 
Nearest. 

Ratio  of 
Lead  to 
Copper. 

I 

2 

.20181 
.  20104 
.  20288 

10 

i 
t 

none 

« 

c% 

775° 

:ll 

.18 

.155 

1000  to  I 

6 

.2OIIO 
.20318 

t 
t 

« 
« 

.20 
.  IO 

.19 

u 

(f 

7* 

.2OIO2 

€ 

10% 

.20 

500  to  r 

8 

.  2OI42 

t 

« 

.20 

« 

9 

JO 

.20138 
.  2OO24 

t 
t 

« 

15% 

.20 
.  II 

.20 

<« 
??•?  to  r 

ii 

.  2OO6O 

i 

It 

.26 

« 

12 
T* 

.  20048 
.  2OIOO 

( 

(I 
20% 

•!5 

•  13 

•  J3 

u 

250  to  i 

14 

.  2OIOI 

( 

« 

.56 

« 

15 

16 

.2Ol6l 
.  2O422 

t 
t 

1C 

25% 

.20 
.28 

.165 

(4 

2OO  tO  I 

17 
18 

.  20296 
20284 

C 
< 

u 

.21 

•3  J 

.25 

« 
ft 

*  Buttons  7-18  gained  in  weight. 

Many  very  interesting  things  are  shown  in  this  series  of  cupel- 
lations.     All  the  gold  beads  showed  the  presence  of  copper  except 


162  NOTES  ON  ASSAYING. 

the  first  series,  in  which  5  per  cent  was  used.  When  10  per  cent 
was  used  the  amount  left  in  the  button  was  a  little  more  than 
the  usual  gold  loss  (.16%)  at  775°,  so  the  buttons,  after  cupellation, 
were  practically  the  original  weights.  -  All  the  buttons  blicked, 
and  even  in  some  tests,  in  which  50%  of  copper  was  used,  a  fair 
blick  was  obtained. 

The  tests  show  with  the  high  ratio  of  1000  of  lead  to  i  of  cop- 
per that  5  per  cent  of  copper  will  be  oxidized  during  cupellation, 
for  the  gold  loss  in  that  series  was  about  normal. 

These  results  are  contrary  to  what  Napier  found,  who  says 
that  ''the  greater  the  amount  of  copper  and  the  greater  the  heat, 
the  more  gold  is  then  lost,  and  that  gold,  when  alloyed  with  copper, 
is  more  volatile  than  when  alone." 

T.  K.  Rose  says:  "If  the  proportion  of  copper  is  increased, 
more  gold  is  absorbed  by  the  cupel." 

Effect  of  Increasing  the  Ratio  of  Silver  to  Gold  upon  the  Loss 
of  Gold. — Some  experiments  given  in  the  first  edition  of  these 
notes  seemed  to  show  that  the  loss  of  gold  during  eupellation 
was  not  diminished  by  the  add-tion  of  ten  or  more  times  as  much 
silver  to  the  assay  as  the  amount  of  gold  supposed  to  be  present 
in  the  ore. 

Further  experiments  indicate  that  the  addition  of  silver  in  large 
excess  does  lessen  this  loss  of  gold. 

Experiments  at  the  Royal  Mint  in  England  show  that  there 
is  almost  always  a  small  amount  of  silver  left  in  the  gold  after 
parting,  that  is,  about  .09  per  cent.  This  is  called  the  surcharge.* 

If  strong  nitric  acid  (1.42  sp.  gr.)  is  used,  this  amount  of 
silver  may  be  slightly  decreased,  but  the  gold  will  begin  to  dissolve. 

Parting  with  Sulphuric  Acid. — When  sulphuric  acid  is  used 
for  parting  it  is  said  that  less  silver  is  left  in  the  gold,  and  no 
gold  is  dissolved.  My  experience  is  that  no  gold  is  dissolved, 
but  silver  is  more  likely  to  be  left  undissolved  than  in  the  treat- 
ment with  nitric  acid.  The  acid  'must  be  boiled  a  long  time 

*  Surcharge,  as  defined  by  T.  K.  Rose,  "is  the  algebraical  sum  of  the  losses  of 
gold  sustained  during  the  various  operations  and  the  amount  of  foreign  substance, 
chiefly  silver,  left  in  the  gold  cornet  when  weighed. 


ASSAY  OF  ORES  FOR   GOLD.  163 

and  even  then  silver  may  be  retained  by  the  gold.     There  are 
also  the  following  disadvantages  in  its  use ; 

1.  It  must  be  used  full  strength,  which  renders  it  liable  to 
bump  violently  when  boiled. 

2.  Lead  and  platinum  are  not  dissolved. 

3.  Difficulty  of  washing  the  gold,  which  must  be  done  very 
carefully. 

4.  Sulphate  of  silver  is  not  very  soluble  in  water;  so  if  much 
silver  is  present  the  first  washings  must  be  made  with  dilute  sul- 
phuric acid. 

SPECIAL  METHODS. 

ASSAY   OF   ZINC-BOX   RESIDUES    FROM   THE   CYANIDE    PROCESS.* 

"  SEVERAL  methods,  both  wet  and  dry,  for  the  assay  of  zinc- 
box  residues  from  the  cyanide  process,  have  been  described  in 
recent  years,  and  each  of  them  has  been  claimed  to  be  superior 
to  all  others.  In  the  year  1901,  a  paper,  entitled  'Assay  of 
Zinc  Precipitates,'  was  published  in  the  School  of  Mines  Quar- 
terly to  the  purport  that  the  scorification  method  for  the  assay 
of  zinc-box  residues  was  absolutely  unreliable. 

In  order  to  shed  light  on  this  matter,  the  following  experi- 
ments were  undertaken  by  Messrs.  C.  B.  Hollis  and  F.  D.  Kehew, 
undergraduate  students  at  the  Massachusetts  Institute  of  Tech- 
nology. 

The  zinc-box  residues  used  were  obtained  through  the  cour- 
tesy of  Mr.  H.  R.  Batcheller.  The  samples  were  very  rich  and 
varied  greatly  in  the  fineness  of  their  condition. 

Scorification  Assays. — In  the  preliminary  tests,  the  charge, 
which  was  weighed  on  a  chemical  balance,  consisted  of  o.i  A.T. 
of  residues  mixed  with  from  30  to  35  grammes  of  test-lead  and 
placed  in  a  3-in.  scorifier,  over  this  an  additional  quantity  of 
test-lead  (from  30  to  35  grammes)  was  placed  for  a  cover,  and 
borax  glass,  varying  in  quantity  from  3  to  15  grammes,  was 
sprinkled  over  the  top  of  each  charge  of  the  various  assays  for  a 
cover.  The  charges  were  scorified  in  a  muffle-furnace  heated 

*  Transactions  American  Institute  of  Mining  Engineers,  October,  1903. 


I  $4  NOTES  ON  ASSAYING. 

to  the  ordinary  temperature  which  is  used  in  scorification ;  in 
some  cases  the  door  of  the  muffle  was  left  open,  while  in  others 
it  remained  closed.  Generally,  the  charges  spit  badly,  espe- 
cially in  the  assays  that  were  made  with  door  of  the  muffle  left 
open,  or  in  those  in  which  the  door  was  opened  too  quickly. 
The  results  of  the  preliminary  assays  showed:  i.  That  in  order 
to  obtain  approximately  uniform  results,  the  material  submitted 
to  the  assay  must  be  in  sufficiently  fine  condition  to  pass  through 
a  2oo-mesh  sieve.  2.  That  the  ordinary  chemical  balances  are 
not  sufficiently  delicate  to  afford  accurate  results  in  handling 
these  residues,  which  are  so  rich  in  gold  and  silver.  3.  That  a 
large  quantity  of  borax  glass  is  absolutely  necessary  (from  3  to  10 
grammes  for  o.i  A.T.  of  residues);  and  4.  That  spitting  can 
be  avoided,  provided  the  muffle  be  heated  to  a  high  tempera- 
ture before  the  introduction  of  the  charge,  and  provided  the 
door  of  the  muffle  be  kept  closed  until  the  contents  of  the  scorifier 
have  become  thoroughly  liquefied;  after  this  the  temperature 
may  be  lowered. 

The  quantity  of  zinc-box  residues  received  amounted  to 
458  grammes,  and,  upon  sizing,  it  was  found  that  146  grammes, 
or  31.8  per  cent,  remained  upon  a  125-mesh  screen;  64 
grammes,  or  13.9  per  cent,  passed  through  a  125-mesh  screen 
and  was  caught  on  a  i6o-mesh  screen;  and  248  grammes,  or 
54.1  per  cent,  passed  through  a  i6o-mesh  screen.  The  entire 
quantity  of  residues  was  then  put  on  a  i6o-mesh  screen,  and 
the  material  that  sifted  through  was  treated  on  a  2oo-mesh 
bolting-cloth,  yielding  290  grammes  of  very  fine  material,  less 
than  2oo-mesh  in  size,  on  which  the  tests  were  made. 

In  order  to  mix  the  sample  thoroughly,  the  entire  quantity 
of  fine  material  was  placed  in  a  38-oz.  bottle  closed  with  a 
glass  stopper  and  steadily  shaken  for  20  minutes,  the  bottle  and 
its  contents  being  alternately  shaken  and  rotated.  The  mixed 
material  was  then  poured  out  upon  a  glazed  paper,  on  which  it 
was  rolled  100  times,  finally  being  spread  out  in  a  thin  layer 
covering  an  area  18  in.  square.  Spatula  samples  to  the  num- 
ber of  450  were  then  taken,  which  constituted  a  new  sample> 
weighing  102  grammes.  A  chemical  analysis  of  the  new  sam- 


ASSAY  OF  ORES  FOR   GOLD.  165 

pie  showed  that  it  contained  9.09   per  cent  of  copper  and  14.3 
per  cent  of  zinc. 

The  assays  were  made  in  a  muffle-furnace  heated  with  coke, 
.and  the  cupels  used  were  of  the  ordinary  bone-ash  variety  made 
at  the  Institute  of  Technology.  Ninety  per  cent  of  the  mate- 
rial forming  the  cupels  was  of  sufficient  fineness  to  pass  through 
an  8o-mesh  screen. 

Four  charges,  Nos.  i,  2,  3,  and  4,  each  of  0.05  A.T.  in 
weight,  were  weighed  on  an  assay  balance  sensitive  to  0.02  of 
a  milligramme  and  treated  as  follows: 

No.  i.  0.05  A.T.  of  the  residues  was  mixed  with  35  grammes 
of  test-lead  in  a  3-in.  scorifier;  30  grammes  of  test-lead  were 
then  added  to  the  top  of  the  charge,  followed  by  a  cover  of  10 
grammes  of  borax  glass. 

No.  2.    The  same  as  No.  i. 

No.  3.  0.05  A.T.  of  the  residues  was  mixed  with  6  grammes 
of  litharge  in  a  3-in.  scorifier.  Additional  test-lead  was  added, 
amounting  to  40  grammes,  followed  by  a  final  cover  of  10  grammes 
of  borax  glass. 

No.    4.     0.05    A.T.    of    the    residues    was    mixed    with    i 
gramme   of   fine   charcoal   and   35    grammes   of   test-lead;     the 
mixture  was  then  covered  with  30  grammes  of  test- 
lead  and  a  final  cover  of  10  grammes  of  borax  glass. 
The  scorifiers  were  placed  in  the  muffle  as  shown  in 
Fig.  i.     The  muffle  was  very  hot  and  the  door  was 
kept  closed  for  about  5  minutes,  after  which  it  was 
opened. 

Charge  No.  i  spit  badly,  doubtless  due  to  its  position  in  the 
muffle;  charge  No.  3  spit  to  a  slight  extent;  while  charges 
Nos.  2  and  4  did  not  spit.  Charge  No.  4  became  covered  over 
very  quickly,  owing  to  the  charcoal  in  the  mixture,  but  the 
resultant  button  of  lead  was  so  large  that  it  was  necessary  to 
rescorify  it.  Although  zinc  ores  require  a  high  temperature 
for  fusion,  the  heat  was  lowered  as  soon  as  possible  after 
the  muffle  was  opened,  in  order  to  slag  off  the  copper  and 
avoid  a  second  scorification.  The  fused  material  poured  well 
.and  the  color  of  the  scorifier  indicated  that  the  buttons  could 


Front. 


i66  NOTES  O.V  ASSAYING. 

be  cupelled  with  safety.  Both  the  slags  and  the  cupels  were 
assayed  by  the  crucible  method,  the  results  being  given  in 
Table  I.  The  silver  and  gold  beads  from  the  slag  of  charges 
Nos.  i  and  2,  and  those  from  the  cupels  used  in  tests'  Nos.  2- 
and  3,  sank  into  the  cupels  which  were  reassayed.  This  addi- 
tional assay  may  account  for  the  low  results  in  silver  and  gold 
that  were  obtained  in  tests  Nos.  2  and  3. 

The  silver-gold  beads  were  weighed,  but,  as  they  did  not 
contain  sufficient  silver  to  part  them,  they  were  recupelled, 
with  the  addition  of  chemically  pure  silver;  the  cupels  of  this 
latter  cupellation  were  not  reassayed.  The  parting  was  done 
with  nitric  acid  of  1.16,  1.20,  and  1.27  specific  gravities.  The 
results  obtained  are  given  in  Table  I. 

Charges  Nos.  5,  6,  and  7,  which  were  similar  in  all  respects 
to  charges  Nos.  i  and  2,  were  next  weighed  and  placed  in  the 
muffle  as  indicated  in  Fig.   2.     The  temperature  of 
the  muffle  was  that  used  in  the  ordinary  assay,  and 
the  door  of  the  muffle  was  kept  closed  for  10  min- 
utes.    It  was  then  opened  and  charge  No.   6  was 
seen  to  spit  twice;    the  door  was  then  closed,  and, 
through  an  opening  in  the  muffle,  charge  No.  6  was 
seen  to  spit  a  third  time.     The  door  of  the  muffle  was  then 
opened   and   the   scorification   completed.     The    slags    and   the 
cupels  from  these  charges  were  assayed  as  in  the  former  tests> 
the  results  being  given  in  Table  I. 

In  order  to  ascertain  whether  a  scorifier  of  larger  size  would 
be  beneficial  or  not,  charge  No.  8  was  assayed  in  a  3-in.  scori- 
fier, and  charge  No.  9  in  a  4-in.  scorifier.  Charge  No.  8  con- 
sisted of  0.05  A.T.  of  residues  placed  in  the  bottom  of  a  3-in. 
scorifier  and  covered  with  65  grammes  of  test- lead,  followed 
with  a  final  cover  of  10  grammes  of  borax  glass.  Charge  No.  9 
consisted  of  0.05  A.T.  of  residues,  prepared  as  in  charges 
Nos.  i,  2,  5,  6,  and  7,  with  the  exception  that  a  4-in. 
scorifier  was  used  in  place  of  a  3-in.  one.  The  tests  were  placed 
in  the  muffle  as  shown  in  Fig.  3.  The  muffle  was  closed  and 
both  charges  were  seen  to  spit  badly.  They  were  then  allowed 
to  become  covered  and  were  later  poured  and  treated  in  a  manner 


ASSAY  OF  ORES  FOR  GOLD.  167 

similar  to  the  earlier  tests.     From  the  results  of  these  tests,  which 

are  given  in  Table  I,  charges  Nos.  8   and   9  were 

rather  peculiar.     The  gold  in  No.  9  was  very  low,  the         IG'  3'c 

silver  was  very  high,  and  an  exceedingly  large  quantity 

of  silver  was  recovered  from  the  slag.     Charge  No.  8, 

also,  showed  a  high  percentage  of  silver  in  the  slag. 

The  cause  of  these  odd  results  was  not  apparent. 

Charges  Nos.  10,  n,  and  12  were  then  made  as  follows: 
Charge  No.  10  consisted  of  0.05  A.T.  of  residues,  60  grammes 
of  test-lead,  10  grammes  of  litharge,  and  12  grammes  of  borax 
glass,  thoroughly  mixed  together  in  a  4-in.  scorifier. 

Charge  No.  n  consisted  of  0.05  A.T.  of  residues  mixed  with 
30  grammes  of  test-lead;  on  this  were  placed  an  additional 
30  grammes  of  test-lead,  followed  by  a  cover  of  10  grammes 
of  litharge  and  a  final  cover  of  12  grammes  of  borax  glass. 

Charge  No.  12  consisted  of  0.05  A.T.  of  residues  mixed  with 
30  grammes  of  test-lead  in  a  4-in.  scorifier,  over  which  were  placed 
30    grammes    of   test-lead   and   a   final   cover   of    14   grammes 
of    borax    glass.     Charges    Nos.     10,     n,    and     12 
were  placed  in  the  muffle  as  shown  in  Fig.  4,  and 
the  door  of  the  muffle  was  kept  closed  for  10  min- 
utes.    Charge  No.  10  fused  very  quietly  and  did  not 
even  tend  to  jump.     Charge  No.  n  was  less  quiet, 
but  did  not  spit,  and  charge  No.  12  was  quiet.     The 
charges  were  allowed  to  become  covered  and  were  then  poured, 
the  resultant  buttons,  slags,  and  cupels  being  assayed  as  in  the 
former  tests.     (See  Table  I.) 

The  results  from  charges  Nos.  n  and  12  were  low,  and  the 
gold  obtained  from  charge  No.  10  was  especially  so.  The  silver- 
gold  button  obtained  from  the  assay  of  the  cupel  used  for  charge 
No.  10  sank  into  the  cupel,  which  had  to  be  reassayed. 

Charge  No.  13  was  similar  to  charge  No.  10,  and  consisted 
of  0.05  A.T.  of  residues,  60  grammes  of  test-lead,  10  grammes 
of  litharge,  and  12  grammes  of  borax  glass,  all  thoroughly  mixed 
together  in  a  4-in.  scorifier. 

Charge  No.  14  consisted  of  0.05  A.T.  of  residues  and  30 
grammes  of  litharge,  mixed  together  in  a  4-in.  scorifier,  and 


i68  NOTES  ON  ASSAYING. 

-covered  with  30  grammes  of  test-lead,  with  a  final  cover  of  12 
grammes  of  borax  glass. 

Charges  Nos.  13  and  14  were  placed  in  a  hot  muffle  in  the 
position  shown  in  Fig.  5.  The  muffle  was  then  closed  for  10 
minutes.  Charge  No.  13  fused  quietly  and  had  no 
tendency  to  spit,  while  charge  No.  14  spit  several 
times  after  the  door  of  the  muffle  was  opened.  These 
charges  were  treated  in  a  manner  similar  to  the  pre- 
vious tests,  except  that,  in  the  assay  of  the  cupel  of 
test  No.  14,  trouble  was  encountered  with  the  silver- 
gold  button,  which  accounts  for  lack  of  results  given  under  this 
heading  in  Table  I.  The  results  for  gold  in  tests  Nos.  13  and  14 
were  low,  an  effect  which  seems  to  be  true  of  all  assay  charges 
containing  litharge. 

A  complete  summary  of  the  data  obtained  in  tests  Nos.  i  to 
14,  inclusive,  are  given  in  Table  I;  and  in  Table  II  are  given 
the  weights  of  the  lead  buttons  and  other  data  relative  to  the 
assays  of  the  slags  and  cupels  of  these  tests. 

A  study  of  the  results  shows  that  the  addition  of  charcoal 
to  the  charge  seems  to  aid  the  scorification.  Also,  that  all  charges 
in  which  litharge  was  used  (Nos.  3,  10,  n,  13,  and  14)  gave  low 
results  for  gold.  The  addition  of  the  litharge,  however,  seemed 
to  prevent  the  spitting  of  the  charge  during  fusion. 

The  value  of  the  residues  in  gold  lies  evidently  between  4690 
and  4698,4  oz.  per  ton,  as  the  results  from  6  of  the  14  charges 
are  within  these  limits,  and  3  of  these  6  are  practically  identical, 
i.e.,  4694  oz.  The  results  for  silver  in  4  of  the  tests  were  between 
4175.2  and  4179.6  oz.  per  ton;  4178.5  oz.  per  ton  being  taken 
for  the  quantity  present. 

Estimating  the  value  of  gold  at  $20.67  Per  oz-  an(^  silyer  at 
$0.50  per  oz.,  the  value  per  ton  of  the  residues  was:  for  gold, 
$97,025,  and  for  silver,  $2,089.  On  tne  basis  of  these  values,  a 
comparison  of  the  highest  and  lowest  content  of  gold  as  deter- 
mined by  the  scorification  method  and  the  percentage  of  varia- 
tion from  the  correct  value  is: — 

Ounces  above,  4.4,  value  $91,  or  0.09  per  cent. 

Ounces  below,  96.8,  value  $2,000.85,  or  2.06  per  cent. 


ASSAY  OF  ORES  FOR   GOLD. 


169 


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NOTES  ON  ASSAYING. 


TABLE  II.—  DATA  OF  ASSAYS  OF  SLAGS  AND  CUPELS  OBTAINED  IN  TREATING  ZINC-BOX 
RESIDUES  OF  TABLE  I. 

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ASSAY  OF  ORES  FOR  GOLD.  171 

The  extremely  low  results  of  test  No.  10  (54.8  oz.,  valued  at 
$1,132.71,  or  1. 1 6  per  cent)  are  omitted  from  this  calculation. 

Summarizing  the  results  of  the  determinations  of  silver  in  a 
similar  manner,  there  were  obtained  the  following  figures: 

Ounces  above,  495.5,  value  $247.7,  or  II-^S  Per  cent- 

Ounces  below,  30.1,  value  $15,  or  0.72  per  cent.  The  high 
results  obtained  in  test  No.  9  (87.9  oz.,  valued  at  $43.95,  or  2-1 
per  cent)  were  not  included  in  this  calculation. 

The  results  for  the  silver  determinations  were  less  uniform 
than  were  those  for  the  gold,  but  the  value  is  apparently  between 
4175  and  4220  oz.  per  ton,  9  results  out  of  the  14  being  within 
this  range.  The  charges  containing  litharge  gave  low  results 
for  silver  in  2  out  of  5  cases. 

The  quantity  of  gold  found  in  the  slags  was  generally  less 
than  that  found  in  the  cupels — a  result  which  is  unusual. 

From  the  results  obtained  in  tests  Nos.  i  to  14,  the  best  method 
for  the  treatment  of  these  zinc-box  residues  is  as  follows: — The 
charge  should  consist  of  0.05  Assay  Ton  of  residues  mixed  with  35 
grammes  of  test-lead  in  a  3  or  a  4-in.  scorifier  and  covered  with 
a  layer  of  30  grammes  of  test-lead,  followed  by  a  final  cover  of 
from  ro  to  1 2  grammes  of  borax  glass.  The  filled  scorifier  should 
be  placed  in  a  hot  muffle  (in  order  that  the  fusion  shall  occur 
rapidly),  and  the  door  should  be  closed  for  fully  5  minutes  after 
the  charge  has  been  fused.  During  the  time  that  the  door  is 
closed,  no  air  whatever  should  enter  the  muffle.  When  the  charge 
has  become  thoroughly  fused,  the  door  of  the  muffle  should  be 
opened  and  the  remainder  of  the  assay  conducted  in  the  usual 
manner. 

Confirmatory  Wet  Assays. — In  order  to  confirm  the  results 
obtained  in  the  scorification  assays,  Mr.  Hollis  made  a  duplicate 
determination  of  gold  and  silver  in  the  zinc-box  residues  by  the 
wet  method  of  Mr.  C.  Whitehead.  These  results  (charges 
Nos.  15  and  16)  were  respectively,  for  gold  =  4698. 8  and  4694.8 
oz.  per  ton;  and  for  silver  =  3841.6  and  "3555.6  oz.  per  ton. 
The  results  for  gold  are  practically  the  same  as  those  obtained  in 
the  scorification  assay.  The  results  for  the  silver,  however, 
are  very  much  lower  and  are  doubtless  due  to  the  incomplete 


172  NOTES  ON  ASSAYING. 

precipitation  of  the  silver  bromide  which  is  soluble  to  a  certain 
extent  in  too  strong  a  solution  of  potassium  bromide.  This 
effect  is  analogous  to  the  action  of  silver  chloride,  for  if  a  solution 
of  silver  nitrate  be  precipitated  by  salt  in  a  solution  that  is  not  suffi- 
ciently diluted,  all  of  the  silver  chloride  will  not  be  thrown  down, 
some  of  it  being  dissolved  in  the  strong  brine. 

The  residues  were  assayed  also  by  the  wet  method  suggested 
by  Messrs.  Charles  H.  Fulton  and  C.  H.  Crawford,*  which  is 
called  the  'combination  wet  and  dry  method  of  assay.' 

The  method  was  used  exactly  as  described,  with  the  excep- 
tion that  the  filter  and  content  were  not  scorified,  but  were  as- 
sayed in  a  glazed  crucible  after  having  been  separately  burned. 
The  data  obtained  by  the  combination  wet  and  dry  method 
are  given  in  Table  III. 

The  data  given  in  Table  III  show  that  the  results  for  gold 
were  somewhat  lower  than  those  obtained  by  the  scorification 
assay,  while  those  for  silver  were  very  much  lower. 

Crucible  Assays. — Three  portions  of  residues  were  taken,  of 
0.05  A.T.  weight,  and  to  each  were  added  15  grammes  of  soda,  10 
grammes  of  borax  glass,  90  grammes  of  litharge,  and  2  grammes 
of  argols ;  an  excessive  quantity  of  litharge  was  used,  in  order 
to  slag  the  copper  and  the  zinc.  The  fusion  was  made  in  a  '  G ' 
crucible,  which  had  previously  been  glazed  with  borax  glass, 
and  each  charge  was  fused  for  35  minutes.  One  charge  ate 
through  the  crucible,  one  would  not  pour,  the  third  only  seeming 
satisfactory.  The  results  of  the  good  test  are  given  in  Table  IV, 
charge  No.  22.  Four  additional  charges  were  made,  Nos.  23, 
24,  25,  and  26,  all  similar  to  No.  22,  with  the  exception  that  the 
•quantity  of  borax  glass  was  increased  to  15  grammes  in  each 
charge.  These  charges  worked  satisfactorily  in  the  furnace, 
but  the  results,  which  are  given  in  Table  IV,  were  not  all  that 
was  hoped  for. 

The  data  given  in  Table  IV  show  that  the  results  for  gold 
and  silver  averaged  much  lower  than  the  quantities  obtained 
in  the  scorification  assays.  The  quantity  of  silver  obtained 

*  School  of  Mines  Quarterly,  January,  1901,  p.   157, 


ASS  A  Y  OF  ORES  FOR   GOLD. 


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174  NOTES  ON  ASSAYING. 

was  very  much  lower,  a  result  which  may  be  due  to  the  large 
quantity  of  litharge  used  in  the  charge,  or  to  the  quantity  of 
copper  present  in  the  sample.  The  slag  also  from  the  crucible 
assay  is  richer  in  both  silver  and  gold,  and  the  second  slags  and 
second  cupels  should  have  been  assayed — an  omission  which 
is  to  be  regretted. 

In  order  to  verify  the  results  obtained  in  the  scorincation 
method  by  Mr.  Hollis,  a  duplicate  set  of  experiments  were  made 
by  Mr.  Kehew  on  residues  from  the  same  lot  of  samples.  Mr. 
Kehew  conducted  the  assays  in  a  muffle  that  was  fired  by  gas, 
and  measured  the  temperature  of  the  experiment  tests  by  a  Le 
Chatelier  pyrometer. 

The  same  care  was  observed  in  taking  the  samples,  and  the 
same  button-balance  was  used  to  weigh  the  samples,  although 
a  different  set  of  assay  weights  was  used. 

Three  charges  were  made,  as  follows:  0.05  A.T.  of  residues 
was  mixed  with  35  grammes  of  test-lead  in  a  3-in.  scorifier;  on 
this  were  placed  30  grammes  of  test-lead  and  a  final  cover  of  10 
grammes  of  borax  glass.  The  charges  were  placed  in  a  very 
hot  muffle,  which  was  of  the  dimensions  12  in.  by  6.25  in.  by  4  in., 
and  the  door  was  closed  for  5  minutes;  the  door  was  then  opened 
and  the  heat  lowered.  No  spitting  took  place.  The  charges 
were  run  so  that  they  were  just  driving,  but  upon  pouring  it  was 
found  that  the  temperature  had  not  been  sufficiently  high  to 
decompose  all  of  the  charge.  The  results  were  therefore  rejected. 
Three  similar  charges  were  then  made,  Nos.  27,  28,  and  29, 
FlG  6  and  placed  in  the  muffle  in  the  position  shown  in  Fig.  6. 
The  test  was  conducted  as  before,  but  at  a  higher 
temperature  (780°  C.  by  pyrometric  measurement). 
The  resultant  lead  buttons  were  too  large  for  cupella- 
>nt'  tion  and  they  were  rescorified,  with  the  addition  of  2 
grammes  of  silica.  The  second  lead  button  was  cupelled,  weighed, 
recupelled,  with  the  addition  of  C.P.  silver,  and  parted  with 
three  strengths  of  nitric  acid,  having  specific  gravities,  respectively, 
of  1. 1 6,  1.20,  and  1.28.  The  results  obtained  are  given  in 
Table  V. 

By  noting  the  position  of  these  charges  in  the  muffle,  it  is 


27 


28 


ASSAY  OF  ORES  FOR   GOLD. 


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i?6  NOTES  ON  ASSAYING. 

seen  that  the  quantity  of  gold  found  in  the  slag  increased  with 
the  increased  temperature,  i.e.,  it  was  greatest  in  the  back  of 
the  muffle  and  least  in  the  front. 

Owing  to  the  fact  that  these  assays  as  conducted  in  a  3-  or 
3.5-in.  scorifier  yielded  a  button  of  lead  which  was  too  large  to 
cupel,  the  subsequent  assays  were  allowed  to  become  covered 
over  with  the  slag,  which  was  then  poured  as  much  as  possible; 
the  scorifier  was  then  replaced  in  the  muffle  and  the  scorification 
continued  until  the  'lead  eye'  was  of  a  diameter  of  0.5  in.;  the 
content  of  the  scorifier  was  then  poured. 

Charges  Nos.  30,  31,  32,  and  33  were  of  the  same  composition 
as  Nos.  27,  28,  and  29,  and  were  placed  in  the  muffle  in  the  po- 
sition shown  in  Fig.  7.     The  slags  from  these  assays 
were  ground,   passed  through  a  4o-mesh  sieve   and 
assayed.     The  buttons  from  two  of  the  assays  passed 
into  the  cupel  and  were  lost;    the  other  two  were 
weighed  and  parted.     The  data  given   in   Table  V 
show  that  more  gold  was  recovered  from  the  slag  in 
tests  Nos.  31  and  33,  which  were  in  the  back  of  the  muffle,  than 
in  Nos.  30  and  32,  which  were  in  the  front.     The  temperature 
in  the  back  of  the  muffle  was  780°  C.,  while  in  the  front  it  was 
720°  C. 

Charges  Nos.  34  and  35  consisted  of  0.05  A.T.  of  residues, 
mixed  with  6  grammes  of  litharge  in  a  3-in.  scorifier,  having 
placed  on  top  40  grammes  of  test-lead,  followed  with  a  cover  of 
10  grammes  of  borax  glass.  The  charges  were  placed  in  a  very 
hot  muffle  and  the  door  closed  for  10  minutes,  after  which  it 
was  opened  and  the  temperature  allowed  to  fall  to  780°  C.  As 
soon  as  the  buttons  had  become  covered,  the  slag  was  poured 
from  them,  but  the  buttons  finally  obtained  were  too  large  for 
cupellation  and  had  to  be  rescorified.  All  slags  and  cupels  were 
assayed  as  usual.  Although  charge  No.  34  was  fairly  satisfactory, 
for  some  unaccountable  reason  the  results  for  charge  No.  35  were 
loo  low. 

Charges  Nos.  36  and  37  consisted  of  0.05  A.T.  of  residues, 
mixed  with  65  grammes  of  test-lead  with  a  cover  of  10  grammes 
of  borax  glass,  and  charges  Nos.  38  and  39  consisted  of  0.05 


ASSAY  OF  ORES  FOR   GOLD. 


177 


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•i  7 8  NOTES  ON  ASSAYING. 

A.T.  of  residues,  with  10  grammes  of  litharge  and  30  grammes 
-of  test-lead,  having  an  additional  quantity  of  30  grammes  of  test- 
lead  placed  on  top  with  a  final  cover  of  10  grammes  of  borax 
glass.  Charges  Nos.  36  and  38  were  placed  at  the  back  of  the 
muffle  and  Nos.  37  and  39  at  the  front.  The  temperature  of 
the  muffle  was  maintained  as  nearly  as  possible  at  790°  C.  Owing 
to  the  door  of  the  muffle  having  been  opened  too  soon,  charges 
Nos.  37  and  39  spit,  the  former  quite  badly.  The  slag  from 
-No.  38,  which  was  at  the  back  of  the  muffle,  contained  more  gold 
than  that  from  No.  39,  which  was  in  front,  but  the  slag  from 
charge  No.  37,  in  the  front,  carried  more  gold  than  that  of  No.  36, 
which  was  at  the  back. 

Considerable  difficulty  was  encountered  in  parting  the  but- 
tons when  the  ratio  of  silver  to  gold  was  2.5  to  i,  even  after  they 
were  annealed  and  rolled  thin.  No  difficulty  resulted,  how- 
ever, when  the  ratio  was  3.5  to  i.  The  data  pertaining  to  these 
assays  are  given  in  Tables  V  and  VI. 

Taking  the  best  results,  i.e.,  charges  Nos.  27,  28,  29,  30,  31, 
32>  33)  36,  and  37,  an  average  of  4699.2  oz.  gold  per  ton  is  ob- 
tained; the  difference  between  the  highest  and  the  lowest  results 
being  18.4  oz.,  which  corresponds  to  0.39  per  cent.  Averaging 
the  results  for  silver  from  these  assays,  the  figure  of  4209.7  oz. 
per  ton  is  obtained;  the  difference  between  the  highest  and  the 
lowest  results  being  29.6  oz.  per  ton,  or  0.7  per  cent. 

In  those  charges  in  which  litharge  was  used,  Nos.  34,  35,  38, 
and  39  (omitting  No.  39),  the  average  determination  of  the  gold 
was  4697.3  oz.  per  ton,  and  of  silver  4202.4  oz.  per  ton. 

A  comparison  of  the  final  average  results  obtained  from  the 
scorification  assays  of  the  zinc-box  residues,  obtained  by  Mr. 
Hollis  and  Mr.  Kehew,  is  given  in  Table  VII. 

Mr.  Kehew  confirmed  his  results  of  the  scorification  assay  by 
the  wet  method  of  Mr.  C.  Whitehead,  as  follows:  0.05  A.T.  of 
the  residues  was  placed  in  a  25o-c.c.  casserole  and  50  c.c.  ol 
water  was  poured  over  it,  followed  by  2 5  c.c.  of  strong  nitric  acid 
(sp.  gr.  1.42).  The  casserole  was  then  placed  on  a  hot-plate  and 
allowed  to  stand  for  2  hours.  The  residue  after  filtration 
.should  have  consisted  of  gold  and  other  insoluble  material,  but 


ASSAY  OF  ORES  FOR   GOLD. 


179 


the  button  obtained  by  cupelling  this  residue  contained  silver, 
which  necessitated  a  second  cupellation,  with  the  addition  of 
C.P.  silver.  The  slags  and  cupels  were  assayed,  the  final  results 
being  given  in  Table  VIII. 

TABLE    VII.— COMPARISON    OF    RESULTS      OF     SCORIFICATION 

ASSAYS  OF  ZINC-BOX  RESIDUES. 
OBTAINED  BY  MR.  HOLLIS  AND  MR.  KEHEW. 


Gold. 

Silver. 

Ounces. 

Value  at  $20.  6  7 

Ounces. 

Value  at  $0.50. 

Mr.  Hollis*  

4694 
4699.2 

5-2 

O.II 

$97025 

97!33 
108 

4i78-5 
4209.7 
31.2 

o-75 

$2089 
2104 
15 

^Mr  Kehew  1" 

Difference  

Difference  percentage.  .  . 

*  Using  coke  fuel. 


t  Using  gas  fuel. 


TABLE  VIII.— DATA  OF  ASSAYS    OF  ZINC-EOX  RESIDUES  BY  THE 
WHITEHEAD  WET  METHOD.     MR.  KEHEW. 


Number  of 
Charge. 

Gold. 

Silver. 

Total  Content. 

Ounces  per  Ton. 

Total  Content. 

Ounces  per  Ton. 

40 
41 

0.23468 
0.23496 

4693  .  6 
4699  .  2 

0.20852 
0.20919 

4170.4 
4183.8 

The  results  for  gold  as  shown  in  Table  VIII  are  not  as  high 
as  those  of  many  of  the  scorification  assays;  the  results  for  silver 
are  quite  a  little  lower,  and  confirm  the  results  obtained  by  Mr. 
Hollis. 

From  the  foregoing  experiments  the  following  conclusions 
may  be  drawn : 

1.  That  the  zinc-box  residues  must  be  in  a  sufficiently  fine 
•state  of  division  to  pass  at  least  through  a  2oo-mesh  screen. 

2.  That  assay-balances,  or  balances  of  equal  delicacy,  must 
t>e  used  for  weighing  the  residues. 

3.  That  the  results  obtained  by  the  scorification  assay,  when 
properly  made,   are   as  accurate  for  the   determination  of  the 
gold  as  those  of  any  other  method  tried,  and  more  accurate  for 


I  So  NOTES  ON  ASSAYING. 

silver  than  the  Whitehead  wet  method  or  the  combination  wet 
and  dry  method. 

4.  That  the  most  satisfactory  charge  is  0.05  A.T.  of  residues, 
mixed  with  35  grammes  of  test-lead  in  a  3-  or  4-in.  scorifier,  with 
30  grammes  of  test-lead  placed  on  top  and  a  final  cover  of  10 
grammes  of  borax  glass. 

5.  That  a  large  quantity  of  borax  glass  is  absolutely  neces- 
sary. 

6.  That  the  spitting  of  the  charge  can  be  avoided  by  placing 
the  scorifiers  in  a  very  hot  muffle,  keeping  the  mufHe  door  closed 
for  at  least  5  minutes  after  the  charge  had  become  fused,  and  then 
opening  the  door  and  reducing  the  temperature  to  from  780°  to 
800°  C. 

7.  That  the  addition  of  a  small  quantity  of  litharge  to  a  charge 
seems  to  lessen  the  danger  of  spitting,  but  when  so  added  the 
results  for  silver  will  probably  be  low." 


ASSAY  OF  COPPER  MATTE,  COPPER  BARS,  OR  COPPER  FOR  GOLD. 

Take  four,  eight,  or  twelve  portions  of  /F  A.T.  or  of  j\  A.T. 
each,  place  in  3"  or  3^"  scorifiers,  and  proceed  through  the 
first  scorification  as  in  Method  II  under  Silver  Assay,  page  50. 
Then,  instead  of  placing  the  lead  button  resulting  from  each 
scorification  in  a  separate  scorifier,  place  four  buttons  in  one 
scorifier,  add  sufficient  lead  to  bring  total  weight  of  buttons  and 
lead  up  to  75  or  100  grammes,  add  1-2  grammes  of  fine  SiO2  and 
2  grammes  borax  glass,  rnd  proceed  as  before.  Continue  scorifi- 
cation until  lead  button  is  fit  to  cupel. 

If  there  is  not  sufficient  silver  present  for  parting,  add  some 
and  cupel  the  lead  button  as  usual. 

Combining  four  lead  buttons  in  this  way  seems  to  give  more 
satisfactory  and  higher  results  than  if  the  four  lead  buttons  are 
carried  through,  separately  and  the  four  silver  and  gold  beads 
parted  together. 

Some  claim  that  the  gold  absorbed  by  the  cupel  is  very  much 
less  where  the  amount  of  silver  added  is  large  than  it  is  when 
just  two  and  one-half  times  the  amount  is  present  or  is  added. 


ASSAY  OF  ORES  FOR   GOLD.  181 

Combination  Wet  and  Dry  Method. — Unless  special  pre- 
cautions are  taken,  this  method  will  give  lower  results  for  gold 
than  the  all-scorification  method. 

Mr.  W.  R.  Van  Liew  has  shown  in  the  Engineering  and 
Mining  Journal,  April  28,  1900,  that  nitrous  acid  (HNO2)  com- 
bined with  HNO3  dissolves  gold,  and  this  more  readily  in  a  hot 
than  in  a  cold  solution.  Nitric  oxide  (NO),  nitrogen  peroxide 
(NO2),  and  nitrogen  trioxide  (N2O3)  combined  with  nitric  acid 
have  no  appreciable  effect  on  gold  whether  the  sqlution  is  hot  or 
cold. 

Mr.  Van  Liew  recommends  the  following  method  for  copper, 
copper  bars,  etc. 

"Take  two  samples  of  i  A.T.  each.  Treat  with  350  c.c.  of 
very  cold  water  and  100  c.c.  of  HNO3  (sp.  gr.  1.42)  in  beakers 
and  set  aside  in  a  cool  place.  The  heat  evolved,  by  the  conver- 
sion of  NO  to  N2O3  and  NO2,  is  considerable,  but  owing  to  the 
bulk  of  water  present  the  temperature  is  kept  down  to  15°  or  16°  C. 
At  this  temperature  and  with  the  degree  of  acid  strength  the 
dissolving  of  the  copper  takes  place  very  slowly.  At  the  end  of- 
1 8  or  20  hours  enough  acid  is  added  to  take  in  solution  the  rest 
of  the  copper;  this  amount  will  vary  front  nothing  to  30  c.c. 
HNO3  (sp.  gr.  1.42),  depending  upon  the  fineness  of  borings  or 
granulations.  At  the  end  of  24  or  26  hours  the  solution  of  the 
•copper  is  complete.  Instead  of  removing  the  lower  oxides  of 
nitrogen  by  boiling  or  heat,  air,  at  a  pressure  of  2  oz.,  is  conducted 
through  a  pointed  glass  tube,  when  the  space  between  the  surface 
of  the  solution  and  the  watch-glass,  clear  until  then,  becomes 
filled  with  the  reddish-brown  fumes  of  N2O3  and  NO2.  At  the 
end  of  20  or  30  minutes  these  lower  oxides  of  nitrogen  are  entirely 
removed.  Any  form  of  hand-blower  can  be  substituted  for  the 
production  of  air  in  place  of  compressed  air. 

"  By  this  method  of  solution  heat  is  applied  at  no  stage  of  the 
process,  and  the  loss  of  gold  is  thus  minimized. 

"  Experiments  having  shown  that  no  difference  was  made, 
whether  the  gold  was  filtered  off  before  or  after  the  addition  of 
the  normal  NaCl  solution,  there  was  added  to  the  cold  solution 
of  Cu(NO3)2  an  excess  of  from  2  to  4  c.c.  of  normal  NaCl  solution, 


iS*  NOTES   QN  ASSAYING.     \ 

besides  that  amount  necessary  to  precipitate  all  the  silver  present. 

"  The  next  morning  the  AgCl  is  filtered  off,  the  entire  contents 
of  the  filter  washed  to  the  point  of  the  filter- paper,  and  the  mass 
of  AgCl  covered  with  4  to  6  grammes  of  test-lead.  The  drained 
papers  are  then  placed  in  2%"  scorifiers,  whose  bottoms  contain 
about  a  gramme  of  test-lead;  the  papers  are  then*dried  and  burned 
in  a  furnace  not  yet  to  a  temperature  of  incipient  redness,  the 
filter- papers  not  being  allowed  to  burn  to  a  complete  ash  in  the 
furnace,  but,  removed  at  the  end  of  the  yellow  flame  of  the  papers,, 
have,  when  they  attain  a  heat  sufficiently  great  to  burn  the  carbon 
of  the  charred  paper  outside  of  the  furnace,  this  slow  combustion 
taking  place  at  a  temperature  too  low  to  cause  any  loss  of  Ag  in 
being  reduced  from  AgCl.  At  the.  end  of  20  minutes  the  papers 
will  have  ashed,  when  no  more  lead  is  added,  but  from  3  to  4 
grammes  of  PbO  and  3  to  4  grammes  of  borax  glass. 

"  The  copper  all  having  been  washed  away  in  transferring  the 
AgCl  to  the  point  of  the  filter,  no  scorification  is  necessary  to  get 
rid  of  any  impurities,  so  this  operation  is  merely  one  of  melting 
and  collecting  the  Ag  and  Au,  the  scorifier  being  poured  as  soon 
as  the  slag  is  hot  enough.  The  resulting  buttons  of  lead  weigh 
from  4  to  5  grammes,  and  are  cupelled  at  a  temperature  giving 
heavy  litharge  feathers,  and  allowed  to  blick  at  the  temperature 
they  are  run,  there  being  no  difficulty  as  to  every  trace  of  lead 
going  off  when  no  other  impurities  are  present.  When  run  this 
way,  duplicates  easily  check  on  the  silvers  within  0.2  and  0.3  oz. 
The  time  of  operation  is  48  hours,  instead  of  24  hours  by  the  usual 
method." 

Results  by  this  method  on  rich  material  should  agree  within 
0.02  or  0.03  of  an  ounce. 

Determination   of    Gold   and    Silver   in    Star  Antimony.* — 

"  First  Method. — Pulverize  fine.  Take  500  grains  and  mix  with 
3000  grains  of  litharge.  Transfer  to  a  small  earthen  crucible  and 
heat  at  a  red  heat  until  the  contents  are  tranquil,  which  will- 
be  about  15  minutes.  The  crucible  is  partly  covered  during  the 
operation. 

*  See  Journal  of  Society  of  Chem.  Industry,  vol.  12,  April  29,  1893,  by  E.  A. 
Smith. 


ASSAY  OF  ORES  FOR   GOLD.  183. 

Pour,  and  when  cold  separate  the  button  from  the  slag,  scorify 
and  cupel.  Weigh  the  button  and  part  in  the  usual  manner.. 
The  slag  may  be  cleaned  by  re-fusing  it  with  some  litharge  and 
charcoal. 

Second  Method. — Take  antimony,  500  grains;  litharge,. 
1000  grains;  nitre,  200  grains;  carbonate  of  soda,  200  grains- 
Fuse  at  a  dull  red  heat  until  quiet,  the  crucible  being  partly 
covered.  Time  of  fusion  about  15  minutes.  The  buttons  of  leadv 
which  should  be  perfectly  malleable  and  weigh  about  500  grains, 
can  be  cupelled  directly.  The  slags  should  be  cleaned  as  in 
first  method.  The  results  are  very  satisfactory,  and  apparently 
more  so  than  in  the  first  method." 

Determination  of  Gold  and  Silver  in  Metallic  Bismuth. — Take 
J  A.T.  or  i  A.T.  of  the  metal  in  the  condition  of  borings  or  of 
chippings  and  cupel  directly.  Bismuth  cupels  as  readily  as  lead,, 
but  the  temperature  should  be  kept  lower. 

Weigh  the  resulting  bead  and  part  in  the  usual  manner. 

One  authority  claims  that  the  bismuth  can  be  recovered  from 
the  cupels  as  follows: 

Break  off  and  discard  all  that  portion  of  the  cupel  not  stained 
by  the  oxide.  Grind  through  an  8o-mesh  sieve.  Fuse  in  a  cru- 
cible with  the  following  charge: 


Mix  thoroughly,  after 
reserving  a  small 
amount  of  soda  and 
borax  to  place  on 
top. 


Cupel  and  bismuth  oxide,    i  A.T. 

Fluorspar 24  grammes 

Na2CO3 12 

Borax 6 

Charcoal. .  .  i         " 


Fuse  as  usual,  pour,  and  weigh  the  resulting  button  of  metallic 
bismuth. 

Assaying  Solutions  containing  Gold. — These  solutions  are 
generally  either  cyanide  or  chloride  of  gold.  Upon  them  I  have 
tried  the  following  methods : 

1 .  Solution  evaporated  with  40  grammes  of  litharge. 

2.  "       3  to  5  grammes  of  silica  and  40 
grammes  of  litharge. 

3.  Solution  evaporated   with  3   to   5   grammes   of  silica,    5 


184  NOTES  ON  ASSAYING. 

grammes  of  borax  glass,  or  10  grammes  borax  and  40  grammes 
litharge. 

4.  Solution  evaporated  with  ^  gramme  soap  and  litharge  and 
silica. 

5.  Solution  evaporated  with  i  gramme  SiO2  and  i  gramme 
of  either  coarse  or  fine  charcoal. 

6.  Solution  evaporated  to  a  very  small  bulk  and  added  to   the 
charge  already  weighed  out  in  a  glazed  crucible. 

7.  Solution  evaporated  in  a  lead-tray. 

The  amount  of  solution  taken  may  be  2  A.T.  to  500  or  1000  c.c., 
depending  upon  the  amount  of  gold  in  the  solution.  In  regard  to 
the  methods,  I  would  say  that  I  have  given  them  to  different 
students,  and  some  find  one  method  most  satisfactory  and  some 
another. 

Methods  i,  2,  and  j. — A  given  amount  of  the  solution  is  evap- 
orated in  a  casserole  or  evaporating-dish  over  a  steam-bath  to 
such  a  small  bulk  that  when  the  SiO2,  litharge,  and  other  reagents 
are  added,  they  absorb  practically  all  the  liquid.  The  contents  are 
stirred  and  heated  until  dry.  The  object  is  lo  keep  the  material 
granular  and  prevent  its  sticking  to  the  dish.  When  dry  it  is  fused 
with  some  soda  and  a  reducing  agent  in  a  crucible  which  has 
been  previously  used,  or  one  glazed  with  borax,  and  the  result- 
ing lead  button,  weighing  26  grammes,  is  cupelled. 

If  any  of  the  residue  sticks  to  the  dish,  it  may  be  removed  by 
rubbing  it  with  a  little  fine  silica  or  glass,  which  is  then  added  to 
the  rest  of  the  charge  in  the  crucible. 

Method  4  is  conducted  in  the  same  manner  as  i,  2,  and  3. 
"The  soap  is  added  to  prevent  spattering. 

Method  5. — This  seems  to  work  especially  well  upon  solutions 
of  AuCl3,  for  the  Au  is  precipitated  in  a  metallic  state  upon  the 
charcoal.  Evaporate  solution  as  in  methods  i,  2,  and  3.  The 
residue  of  charcoal  and  silica  is  then  mixed  with  soda  and 
litharge,  which  have  been  weighed  out  in  a  glazed  crucible  and 
the  charge  fused.  The  little  particles  of  gold,  in  this  case,  are 
in  direct  contact  with  the  carbon,  as  it  reduces  lead  and  it  makes 
a  most  satisfactory  fusion.  Coarse  charcoal  seems  preferable 
to  fine. 

Method  6. — This  is  the  least  reliable,  because,  unless  the  cru- 


ASSAY  OF  ORES  FOR   COLD. 


185 


cible  is  well  glazed  and  shows  no  cracks,  some  absorption  by  the 
crucible  will  take  place. 

M'ethod  7. — If  the  solution  contains  only  salts  of  gold  and  is 
not  acid,  this  method  seems  preferable  to  any  of  the  preceding, 
because  the  lead  tray  and  its  contents  can  be  cupelled  directly. 
If  the  solution  is  acid,  it  will  of  course  corrode  the  tray,  and  if 
many  salts,  like  CaSO4  are  present,  the  tray  and  contents  can- 
not be  cupelled,  but  will  have  to  be  scorified,  which  of  course  is 
not  desk-able  in  an  assay  for  gold.  Test  the  lead-tray  with  water 
to  see  if  it  is  tight  before  adding  the  solution.  Towards  the  end, 
when  little  solution  is  left,  the  lamp  should  be  turned  out. 

In  any  of  the  methods  where  the  solution  is  evaporated  and 
the  residue  transferred  to  a  crucible,  the  most  important  thing 
is  to  see  that  this  residue  does  not  stick  hard  to  the  vessel  in 
which  the  evaporation  has  taken  place.  A  slight  adhesion  does 
no  harm,  for  this  can  easily  be  removed  by  rubbing  the  vessel 
with  a  little  fine  silica. 

If  the  solution  is  very  poor  in  gold,  it  will  be  necessary  to  add 
C.P.  Ag  when  cupelling  and  then  part  the  resulting  button.  If 
the  solution  carries  both  Au  and  Ag,  a  separation  will  of  course 
have  to  be  made. 

Some  results  obtained  are  as  follows: 


Lot  A. 

LotB. 

Run  VI. 

LotC. 

Method. 

Gold  in 
150  c.c. 
KCy,  AuCy. 
Grammes. 

Method. 

Gold  in 

200  C.C. 

Grammes. 

Method. 

Gold  in 

200  C.C. 

Grammes. 

Method. 

Gold  in 

200  C.C. 

AuCl3. 
Grammes. 

I 

.00115 

I 

.  00296 

2 

.00474 

I 

.01089 

2 

.00117 

2 

.  00290 

2 

.00470 

I 

.01088 

6 

.00114 

6 

.  00298 

2 

.  00478 

I 

.01090 

2 

.00474 

The  results  in  Lot  C  were  checked  by  precipitating  the 
gold  from  200  c.c.  of  solution  with  FeSO4,  which  gave  .01087 
grammes  as  an  average  of  four  determinations,  and  also  by 
H2S,  which  gave  .01084  grammes  as  an  average  of  three  determin- 
ations. 

The  gold  in  a  solution  of  AuCL,  can  also  be  determined  by 


1 86  NOTES  ON  ASSAYING. 

throwing  it  down  by  means  of  H2S,  FeSO4,  oxalic  acid,  or  alumin- 
ium-foil. 

Filter  on  a  small  filter,  and  while  the  filter-paper  and  contents 
are  still  moist  wrap  in  C.P.  sheet  lead  and  cupel  with  or  without 
the  addition  of  C.P.  Ag,  as  it  seems  best. 

The  cupelling  is  most  successfully  done  by  having  a  cupel  very 
hot,  bringing  it  out  to  the  mouth  of  the  muffle  and  then  dropping 
in  the  C.P.  lead  and  contents.  Allow  the  filter  to  burn  slowly, 
and  gradually  push  the  cupel  back  into  the  muffle  until  the  lead 
begins  to  drive.  If  any  little  pieces  of  lead  appear  on  the  sides 
of  the  cupel,  tip  the  cupel  and  collect  them. 

Electrolytic  Deposition. — This  is  probably  the  most  accurate 
of  any  of  the  methods,  and  either  solutions  of  AuCN,KCN  or 
AuCl3  can  be  valued  by  it. 

AuCNjKCN  Solution. — Take  the  same  amount  of  solution  as 
in  the  other  methods  and  evaporate  to  100  or  125  c.c.  For  elec- 
trodes take  thin  pieces  of  C.P.  lead-foil  and  attach  to  platinum 
wires.  Keep  the  Pt  wires  out  of  the  solution. 

Use  about  .05  to  .12  amperes.     Allow  to  run  overnight. 

The  lead  cathode,  with  deposited  metals,  is  then  detached, 
placed  on  a  piece  of  C.P.  sheet  lead,  wrapped  up  tightly,  and 
cupelled  directly. 

The  following  are  some  comparative  results: 

Solution  No.  2.  Solution  No.  15. 

AuCN.KCN  AuCN.KCN 

(150  c.c. ).  (150  c.c.). 

Electrolytic Gold  .054  oz.  Silver   .381  oz.         Gold  i  .35  oz. 

Evaporation  with  PbO  and 

silica "     .05802.  "        .38502.  "    1.3502. 

Chiddey's  Method. — Mr.  Alfred  Chiddey*  suggests  the  fol- 
lowing: "  Introduce  into  a  porcelain  dish  4  A.T.,  or  mo"e, 
of  the  solutions  to  be  assayed,  add  10  c.c.  of  a  10  per  cent 
solution  of  acetate  of  lead,  then  4  grammes  of  zinc  shavings; 
boil  a  minute,  add  20  c.c.  of  HC1.  When  the  action  has  ceased, 
boil  again;  wash  the  spongy  lead  with  distilled  water;  transfer 
it  with  a  stirring- rod  to  a  piece  of  filter-paper;  squeeze  into  a 
compact  lump  and  place  in  a  hot  cupel. 

*  Eng.  and  M.  J.,  March  28,  1903,  p.  473. 


ASSAY   OF  ORES  FOR   GOLD. 


187 


"The  mouth  of  the  muffle  should  contain  a  piece  of  dry  pine 
wood,  so  that  the  muffle  is  filled  with  flame  at  the  moment  of 
introducing  the  spongy  lead. 

"  In  the  case  of  very  dilute  nearly  pure  gold  solutions  I  would 
suggest  the  addition  of  a  known  quantity  of  nitrate  of  silver  dis- 
solved in  cyanide  before  adding  the  acetate  of  lead." 

The  following  are  some  comparative  results : 


Evaporation  with 
Litharge,  Soda, 
and  Charcoal. 

Evaporation  in  a 
Lead  Tniy. 

Chiddey's  Method. 

150    cc.    of    a    solution    of 
AuCN.KCN  

100  cc.  of  AuCN,KCN.  .  .  ] 

loocc.  of  AuCN,KCN.... 
50  cc  of  AuClo  

Gold      .  59  oz. 
Gold    i  23  " 

Gold     1.9802. 
Silver  4.06  " 
Gold       .20  " 

Gold       .  59  oz_ 
Gold    2.01  " 
Silver  3  .  98  " 
Gold      .21  " 
Gold    i   17  tc 

My  experience  with  this  method  is  that,  as  a  rule,  it  is  a 
most  excellent  one  and  by  far  the  shortest  of  any  suggested  up> 
to  this  time.  The  following  additional  data  may  prove  helpful. 
Always  roll  the  zinc  shavings  lightly  into  a  ball  between  the 
hands  so  as  to  have  them  compact  with  few  ends  protruding. 
Care  must  be  taken  to  have  sufficient  lead  acetate  present;  15  to 
20  c.c.  are  none  too  much  for  a  large  amount  of  solution  or  for 
one  rich  in  precious  metals.  Have  sufficient  HC1  (sp.  gr.  1.2) 
present  to  dissolve  the  zinc,  but  not  much  in  excess.  The  lead 
thrown  down  should  enclose  the  zinc  completely,  otherwise  the 
latter  will  break  up  into  fine  threads,  rendering  it  necessary  to 
filter.  The  presence  of  copper  in  the  solution  seems  harmful, 
causing  the  zinc  and  lead  to  break  up  and  become  £ncly  divided. 
In  many  solutions  the  spongy  lead  thrown  down,  when  placed 
on  the  cupel,  is  not  sufficient  to  collect  the  precious  metals  into 
one  bead,  so  I  prefer  to  wrap  it  in  lead-foil  and  then  cupel.  On 
gold  chloride  solutions  the  method  seems  to  give  low  results. 
Heating  this  solution  decomposes  it,  throwing  down  metallic  gold, 
which  makes  filtering  necessary,  so  the  solution  must  be  kept 
cold. 


1 88  NOTES  ON  ASSAYING. 

The  following  are  some  other  methods  which  have  been 
suggested  for  valuing  cyanide  solutions  for  gold : 

"Take  15  A.T.  or  more  of  solution,  add  15  to  25  c.c.  of  strong 
H2SO4  and  6  to  12  grammes  of  zinc-dust.  Warm  and  stir  at 
intervals  for  at  least  10  to  12  hours.  Dissolve  any  zinc  remaining 
and  then  filter.  Burn  the  filter  in  a  crucible  containing  part  of 
the  flux  for  the  crucible-charge,  cover  with  the  remaining  flux 
and  some  borax  glass,  fuse  and  assay.  Sufficient  time  must 
be  allowed  in  this  method  in  order  to  be  sure  that  all  the  gold 
lias  been  precipitated." 

Miller's  Method.     E.  &  M.  J.,  July  23d,  1904,  p.  997. 

"Take  1000  c.c.  of  solution  and  put  in  a  2-litre  flask.  Add 
i  to  2  grammes  of  powdered  copper  sulphate.  Agitate.  Add 
10  to  15  c.c.  of  concentrated  HC1  and  agitate  thoroughly.  Filter, 
dry  the  precipitate  on  the  filter,  burn  and  assay  the  precipitate 
either  in  a  crucible  or  scorifier,  preferably  the  former." 

Lindeman's  Method.     E.  &  M.  J.,  July  yth,  1904,  p.  5. 

"Ten  A.T.  of  solution  are  heated  until  quite  hot,  ammoniac  1 
copper  nitrate  is  then  added  until  the  solution  shows  a  permanent 
blue  color.  Sulphuric  acid  is  then  carefully  added  in  excess, 
the  solution  stirred  and  immediately  filtered.  The  paper  is 
folded  and  carbonized  in  a  scorifier,  transferred  to  a  crucible, 
fused  and  cupelled." 

Arent's  Method.     A.  I.  M.  E.     Albany  meeting,  Feby.  1903. 

"Take  250  c.c.  of  the  solution  to  be  tested;  add  a  few  c.c.  of 
H2SO4;  agitate  for  several  seconds  and  then  add  not  less  (al- 
though not  much  more)  than  one  gramme  of  cement-copper. 
Heat  to  boiling.  This  is  kept  up  for  about  10  minutes,  so  that 
the  rising  steam-bubbles  keep  the  mixture  well  agitated.  The 
mixture  is  then  filtered  through  a  y-inch-diameter  gray  filter- 
paper.  No  washing  is  done.  As  soon  as  the  filtering  is  finished, 
one-third  of  a  crucible-charge  of  flux  is  added  to  the  filter  con- 
taining all  the  sediment  of  the  mixture.  Some  of  the  moisture 
is  rapidly  absorbed  by  the  flux,  which  permits  the  folding  of 


ASSAY  OF  ORES  FOR   GOLD.  189* 

the  filter's  rim  upon  the  charge  and  its  subsequent  removal 
without  loss  or  tearing.  One-third  of  a  crucible-charge  of 
flux  having  previously  been  placed  upon  the  bottom  of  the 
crucible  which  is  to  be  used  for  melting,  the  filter  is  trans- 
ferred to  the  crucible,  well  tucked  down,  and  the  last  one-third 
of  the  crucible-charge  is  placed  on  top  of  the  filter  in  the  crucible. 
It  is  then  ready  for  the  furnace.  The  filter  furnishes  the  reduc- 
ing-agent  for  the  assay." 

"Use  30  grammes  litharge  and  the  usual  amount  of  borax 
and  soda,  employing  an  F  crucible  for  melting.  About  20 
grammes  of  lead  are  obtained  which,  upon  cupelling,  furnishes. 
a  bead  free  from  copper." 

The  use  of  precipitants  other  than  copper  and  copper  salts 
seems  to  me  advisable,  because  with  copper  we  are  making  use 
of  a  metal  known  to  be  deleterious  in  the  cupellation  process  and 
one  which  we  especially  endeavor  to  eliminate  beforehand. 


CHAPTER  V. 
ASSAY  OF  ORES  FOR  LEAD. 

LEAD  fuses  at  327°  C.,  sp.  gr.  =  11.35,  atomic  weight  =  206.95. 
The  principal  ores  of  lead  are: 

Galena,  PbS  (sp.  gr.  7.4  to  7.6),  with  86.6%  lead  when  pure. 
Cerussite,  PbCO3  (sp.  gr.  6.46  to  6.57),  with  77 J%  lead  when 
pure. 

Anglesite,  PbSO4  (sp.  gr.  6.12  to  6.39),  with  68.3%  lead  when 
pure. 

Pyromorphite,  3PbO,P2O5+PbCl2  (sp.  gr.  6.5   to  7.1),  with 
76.3%  lead  when  pure. 

Besides  these  we  have  many  complex  compounds,  such  as 
Bournonite,  PbS  +  Cu2S+Sb2S3  (sp.  gr.  5.7  to  5.9). 
Jamesonite,  2PbS+Sb2S3  ("     "    5.5  to     6). 

While  the  assayer  may  be  given  ores  or  concentrates  similar 
to  the  first  four,  he  usually  has  submitted  to  him  ores  or  products 
of  a  much  more  complex  and  a  much  baser  character,  such  as 
PbS+FeS2+PbCO3  in  a  quartz  or  silicious  gangue; 
PbS+ZnS+FeS2         "  "  calcareous  or  silicious  gangue; 
PbS+  PbCO3  "  "  calcareous  gangue. 

He  may  also  have  submitted  to  him  furnace  products,  litharge 
(92.86%  lead  when  pure,  sp.  gr.  9.2  to  9.36),  old  cupels,  slags, 
etc.     Although  the  fire  assay  for  lead  is  less  accurate  than  the 
wet  method,  still  it  is  in  general  use  at  smelting  works  for  assay- 
ing ores  and  furnace  products,  because  lead  ores  are  always  bought 
and  sold  on  this  assay  and  not  upon  the  wet  analysis. 
The  reasons  for  its  inaccuracy  are  the  following: 
i st.  Because  lead  and  lead  sulphide    are    both  volatile  at 
moderate  temperatures.     Results  low. 

190 


ASSAY  OF  ORES  FOR  LEAD.  191 

2d.  Because  impurities  of  various  kinds  (Cu,Sb)  are  reduced 
with  the  lead  and  pass  into  the  button.  Results  high. 

3d.  Because  of  the  tendency  that  lead  and  its  compounds 
have  to  slag,  which  tendency  is  increased  by  the  presence  of 
arsenic,  antimony,  and  zinc.  Results  low. 

For  these  reasons  we  must  be  especially  careful  of  the  heat,  and 
the  slag  must  be  made  as  simple  as  possible,  easily  fusible,  and 
must  not  be  too  acid. 

For  convenience,  lead  ores  may  be  divided  into  — 

i  st.  Those  which  contain  sulphur. 

2d.  Those  which  do  not  contain  sulphur. 

Our  object,  in  either  class,  is  to  flux  the  gangue  of  the  ore 
and  reduce  the  lead  present,  from  whatever  combination  it  may 
be  in,  to  metallic  lead;  therefore  the  simpler  we  are  able  to  make 
the  fluxes  the  lower  we  may  keep  the  heat,  and  the  shorter.  the 
time  of  fusion  the  better  it  will  be.  Keep,  however,  in  mind 
that  the  ore  must  be  decomposed  and  the  slag  perfectly  liquid. 

The  ores  should,  like  those  for  the  assay  of  silver  and  gold, 
be  fine  enough  to  pass  through  a  loo-mesh  sieve  and  should  have 
been  dried  at  100°  C. 

Make  all  fusions  in  a  muffle-  furnace,  unless  specified  otherwise, 
and  report  the  results  in  percentage  to  first  place  of  decimals. 

The  assay  consists  of  a  reducing  fusion  with  iron  and  some 
reducing  agent,  such  as  argols,  charcoal,  flour,  etc.  The  reducing 
agents  take  away  the  oxygen  from  the  PbO  present  or  formed 
during  the  fusion,  and  the  iron  removes  the  sulphur  : 

PbS+Fe  =  FeS+Pb. 


Nails,  iron,  or  iron  crucibles  are  absolutely  necessary,  whether 
there  is  sulphur  present  in  the  ore  or  not,  for  three  reasons: 


By  adding  iron  we  obtain 

(K2S,PbS)  -h  Fe  =  (K2S,FeS)  +  Pb. 

That  is,  if  iron  was  not  present,  the  double  sulphide  of  lead 
and  the  alkali,  used  as  a  flux,  would  pass  into  the  slag  giving 
low  results. 


192  NOTES  ON  ASSAYING. 

2.  PbS+Fe  =  FeS+Pb. 

3.  2PbO,SiO3+2Fe  =  2Fep,SiO2+2Pb. 

The  siliceous  impurities  are  generally  quartz,  feldspar,  and 
complex  silicates ;  the  basic  ones  are  limestone  and  oxide  of  iron. 
The  gangue  may  also  be  barite  and  sometimes  fluorspar. 

The  fluxes  employed  are  sodium  or  potassium  carbonate  for 
the  silica,  borax  glass  for  the  oxides  and  limestone,  fluorspar  for 
barite,  argols  or  charcoal  for  a  reducing  agent,  and  iron  as  a 
desulphurizer. 

In  this  assay,  as  in  the  assay  of  ores  for  silver  and  gold,  we 
find  the  following: 

Silver  and  gold  in  the  ore  both  pass  into  the  lead  button. 

Copper  goes  partly  into  the  lead  and  partly  into  the  slag;  a 
high  temperature  and  a  great  excess  of  reducing  agent  will  tend 
to  make  it  pass  into  the  lead. 

Zinc  partly  volatilizes,  partly  slags,  and  a  small  quantity  passes 
into  the  lead. 

Antimony  goes  partly  into  the  slag,  but  most  of  it  into  the  lead- 

Arsenic  (depending  upon  the  temperature  of  the  fusion)  either 
forms  a  speiss  with  the  iron  present  or  else  partly  slags  and  partly 
volatilizes.  (See  page  137  )  This  speiss  is  lighter  than  the  lead 
and  will  be  found  as  a  round  brittle  button  on  top  of  or  embedded 
in  the  lead.  From  the  foregoing  data  it  will  be  seen  that  if  our 
ore  is  very  impure,  that  is,  if  it  contains  much  Cu,  Sb,  or  As,  our 
results  will  be  rather  unsatisfactory.  In  ores  of  this  character  we 
have  to  resort  to  the  wet  analysis. 

Sulphide  Ores.  (Fusion  in  the  muffle.) — Sulphate  of  lead, 
either  natural  (anglesite)  or  obtained  from  chemical  works,  is- 
treated  in  the  same  manner. 

It  is  recommended  to  use  at  least  10  grammes  of  the  material 
to  be  analyzed  and  if  possible  20,  for  my  experience  is  that 
10  grammes  give  better  results  than  5,  and  20  oftentimes  better 
than  10. 

The  following  proportions  of  fluxes  to  ore  will  serve  as  aa 
example  for  our  assays.  Refractory  sulphides,  like  sulphide  of 
zinc  and  those  with  a  basic  gangue,  will  probably  require  an  addi- 
tional amount  of  borax  glass. 


ASSAY  OF  ORES  FOR  LEAD. 


Ore 10-20  grammes 

NaHC03  .20-40 


* 


3  .- 
25-50  or  \  __  ^^ 

(  K2CO3.  .     5-10 


Mix 
.  , 
in  the 

crucible.. 


Borax  glass 8-10 

Argols 5-5 

Nails  (tenpenny) 5-5 

or  one  rail- spike  (2  J"  or  3"  long) 

Cover  salt  -J"  deep  if  possible. 

The  soda  and  potash,  besides  acting  as  fluxes,  probably  act  ii> 
this  way :  K2CO3  =  K2O  +  CO2 ;  PbS + K2O  +  C  =  K2S  +  CO  +  Pb. 

If  the  borax  glass  is  used  in  too  large  quantity,  it  will  make  the 
slag  too  acid,  and  the  lead  will  pass  into  it.  In  a  clean  galena, 
we  shall  need  only  a  gramme  or  two,  while  in  limestone  carrying 
PbS  or  in  an  ore  carrying  much  ZnS  we  shall  require  as  much  as 
6  or  8  grammes.  In  place  of  nails  as  a  desulphurizer,  some  assay- 
ers  use  coils  of  coarse  wire  or  a  strip  of  broad  iron  bent  on  the 
curve  of  the  crucible.  Using  5  grammes  of  ore  has  always  given 
me  lower  results  than  when  using  10  grammes.  If,  however,  5. 
grammes  are  used,  diminish  the  soda  and  borax  glass  a  little,  but 
keep  the  argols  and  the  nails  the  same. 

Fusion  in  the  Muffle. — Place  the  crucible,  by  means  of  a  pair 
of  tongs,  in  a  good  hot  muffle  and  close  the  door  of  the  muffle 
with  a  plate  or  with  some  charcoal  or  with  both.  When  the  con* 
tents  of  the  crucible  begin  to  fuse,  which  is  indicated 
by  small  jets  of  flame  leaping  up  from  the  interior  of 
the  crucible,  close  the  draft  of  the  furnace  and  lower 
the  temperature,  to  prevent  the  contents  of  the  crucible 
from  boiling  over.  When  the  danger  of  this  is  over, 
keep  the  muffle  closed  and  the  heat  at  scorifying  temper- 
ature or  lower  for  30  minutes,  then  raise  the  temperature 
for  1 5  to  20  minutes  more  to  the  greatest  temperature  of 
the  muffle.  The  whole  period  of  fusion  should  be  from 
35  to  55  nr'nutes,  depending  upon  purity  of  the  ore  and 
the  character  of  its  gangue.  Take  the  crucible  from  the  furnace,. 
but  do  not  set  it  down,  catch  the  nails  with  a  pair  of  small  hand- tongs,, 
tapping  them  gently  while  holding  them  in  the  slag,  then  remove. 

*  With  10  grammes  of  ore  use  A,  and  with  20  grammes  of  ore  use  B  crucible. 


194  NOTES  ON  4SS4YING. 

(If  drops  of  lead  are  on  the  nails,  return  crucible  to  muffle,  for  the 
fusion  is  incomplete.)  Pour  the  fusion  into  a  mould  and  when  cold 
separate  the  lead  from  the  slag  and  hammer  clean.  Weigh  to 
second  place  of  decimals  and  report  the  result  in  percentage.  Dupli- 
cate assays  should  agree  within  one  half  of  one  per  cent,  and  a 
pure  galena  should  give  83^%  to  84%  of  lead. 

The  following  fluxes  may  be  used  in  place  of  soda  and  argols  : 

White  Flux,  made  by  deflagrating  together  equal  parts  of 
saltpetre  and  argols. 

Black  Flux,  made  by  deflagrating  together  one  part  of  saltpetre 
with  two  or  three  parts  of  argols. 

Black  Flux  Substitute  is  a  mixture  of  ten  parts  of  carbonate  of 
soda  and  one  to  three  parts  of  flour. 

Cyanide  of  Potash  Method.  (Fusion  in  the  muffle.)  —  This 
method  has  one  great  advantage  over  any  of  the  preceding  ones, 
in  that  it  can  be  done  at  a  much  lower  temperature.  Still  it 
seems  to  give  lower  results  than  the  ordinary  muffle  assay  or  the 
iron-crucible  assay,  which  may  be  due  to  the  KCN  holding  some 
lead  sulphide  in  solution  The  charge  is  made  up  as  follows: 

Ore,  10  grammes;  KCN  25  grammes.  Mix.  (The  KCN  is 
a  deadly  poison  !)  Fuse  for  25  minutes  at  a  low  temperature  and 
look  out  for  fumes: 


=  Pb+KCNO,   also   PbS  +  KCN  =  Pb  +  KSCN. 

Sulphide  Ores.  (Fusion  in  pot-furnace.)  —  These  ores  may 
be  assayed  in  this  way,  using  the  same  or  larger  quantities  of  ore 
and  fluxes  as  were  used  in  the  muffle  assay.  The  method  is  much 
more  difficult,  however,  and  great  care  has  to  be  exercised  in  the 
heat,  otherwise  the  loss  by  volatilization  will  be  very  great. 

When  we  have  a  rich  or  fairly  pure  ore  we  can  make  an  assay 

Qin  an  iron  crucible  to  great  advantage.  The  crucible,  which 
should  be  of  very  heavy  wrought  iron,  takes  the  place  of  the 
nails  and  acts  as  the  desulphurizer. 

Slags,  Furnace  Products,  or  Ores  Very  Poor  in  Lead.  (Fusion 
in  pot-furnace.)  —  These  can  be  assayed  to  advantage  in  the  pot- 
furnace,  for  we  can  use  a  large  quantity  of  slag  or  of  ore.  Use  E 
or  F  crucible. 


ASSAY  OF  ORES  FOR  LEAD. 


195 


The  following  charges  I  have  found  to  work  very  satisfactorily : 


Slag  ............  30    grammes 

Bicarb,  soda  .....  60 

Borax  glass  ......  o  to  5       " 

Argols  ..........        6 

Nails  (20penny).  .        i 


Mix 


or  Spike  ......        i 

Cover  of  salt  i£ 


thick. 


Ore 30  grammes 

(Limestone  carrying  £  to  2%  of  PbS) 

Bicarb,  soda 60  grammes 

Borax  glass 15        " 

Argols 8 

Nails  (2openny) 2 

or  Spike i 

Cover  of  salt  i"  thick. 


Keep  in  the  furnace  25  to  35  minutes  after  the  fusion  has  taken 
place.  Results  by  the  above  fusions,  on  low-grade  ores  or  slags 
running  from  2  to  5  per  cent,  check  very  closely  (.2%  to  .3%). 
If  the  ore  is  so  poor  that  no  lead  button  is  obtained,  200  or  more 
grammes  of  it  can  be  taken,  panned,  and  the  concentrates 
assayed.  From  this  assay  figure  the  amount  of  lead  in  the 
original  ore. 

The  method  of  adding  a  known  amount  of  silver  to  the  slag 
to  be  assayed  and  then  subtracting  this  from  the  lead  button 
obtained  I  have  found  inaccurate  and  unsatisfactory,  also  the 
method  of  adding  a  given  quantity  of  PbO  and  allowing  for  the 
lead  contained  therein. 

Sulphide  Ores  in  Iron  Crucible.  (Fusion  in  pot-furnace.) — 
Ores  should  be  quite  pure. 

Place   in  the 

Ore 50     grammes  f.  bottom  of  the 

crucible. 


Potash  (K2CO3) 50-75 

Borax  glass 8-10 

Flour 8 

Cover  of  salt  iV  thick. 


Mix  and 

place  upon 

the  ore. 


If  25  grammes  of  ore  are  taken,  use  only  5  to  6  grammes  of 
borax  glass,  30  of  potash,  and  5  of  flour. 

Fuse  for  about  12  minutes  or  until  fairly  quiet,  that  is,  until 
foaming  ceases.  Take  the  crucible  from  the  furnace,  let  it  cool 
a  minute  or  so,  and  then  pour  as  usual. 

Class  II.  Ores  Containing  no  Sulphides.  (Fusion  in  the 
muffle.) — Although  these  ores  may  be  assayed  in  the  pot- furnace, 
the  student  is  recommended  to  use  a  Battersea  A  or  B  crucible, 


NOTES   ON  ASSAYING. 


or  one  similar  in  size,  and  make  the  assay  in  the  muffle.  Conduct 
the  assay  as  in  Class  I  (muffle  fusion).  Mix  the  ore  with  the 
fluxes,  but  never  have  the  crucible  more  than  two  thirds  full. 
For  substances  given  below  use  the  following: 


No.  i. 

No.  2. 

No.  3. 

No.  4. 

No.  5. 

Lead 

Lead 

Carbon- 
ate. 

and 
Copper 
Carbon- 

Cupels. 

Lead 
Phos- 
phate. 

Lead 
Silicate. 

ate. 

Ore,                 grammes   . 

10-20 

IO-20 

10    or    10-20 

io—  20 

10-20 

Birarb.  soda,        " 

I5~I5 

IO 

20                      10 

3° 

20 

"        potash,     " 

5-10 

15 

10 

— 

Lorax  glass,         " 

3-  3 

5 

10                      10 

5 

2 

Argols, 

7~  7 

4 

8Q 
0 

5 

5 

Sulphur,               " 

I 



Nails  (ten  penny),  or  one 

3~  3 

— 

3                 3 

2 

3 

rail-rpike  23—  3"  long 

Cover  of  i\"  of  salt  in  each  case. 

Ores  containing  MnO2  or  Fe2O3  require  an  additional  quan- 
tity of  argols.  A  mixture  of  carbonate  of  soda  and  carbonate  of 
potash  is  more  fusible  than  either  one  alone. 

In  the  phosphate  ore,  phosphate  of  soda  and  PbO  form; 
the  argols  then  act  and,  as  in  all  the  other  cases,  reduce  the 
PbO  to  Pb.  Iron  is  used  in  all  the  charges  except  in  No.  2.  It 
is  used  in  the  silicate  because  lead  is  not  easily  reduced  from  sili- 
cate of  lead  except  in  the  presence  of  iron.  Sulphur  partly  de- 
composes the  singulo-silicate,  and  carbon  reduces  some  of  the  lead 
from  a  bisilicate,  but  in  order  to  extract  all  the  lead  it  must  be 
set  free  by  a  basic  flux,  and  this  is  the  reason  that  metallic  iroix 
sets  free  all  the  lead  from  all  fusible  lead  silicates: 


2FeO,SiO2+2Pb. 

This  is  probably  the  reason  why  in  the  assay  of  cupels  and 
other  non-sulphide  substances  we  obtain  higher  results  when  iron. 
is  used  than  when  it  is  not,  for  silicate  of  lead  is  either  present 
or  it  is  formed  during  the  fusion  from  the  ingredients  of  the 
crucible  itself  and  the  PbO,  or  from  the  gangue  of  the  ore  and 
the  PbO. 

A  bright  button,  separating  easily  from  the  slag,  indicates  too* 
great  a  heat  or  too  long  a  fusion.  A  bright  coating  between  the 
button  and  the  slag  indicates  too  low  heat  or  imperfect  decom- 
position. 


ASSAY  OF  ORES  FOR  LEAD.  197 

Cu,  As,  Sb,  Zn,  or  S  may  cause  buttons  to  be  brittle. 

Cu  and  Sb  may  cause  them  to  be  hard. 

General  Remarks  upon  the  Lead  Assay. — As  has  been  previ- 
ously stated,  it  seems  advisable  to  use  as  much  of  the  substance  as 
possible  for  the  assay  without  filling  an  A  or  B  crucible  more  than 
two  thirds.  In  the  West  they  formerly  used  5  grammes,  but  the 
writer  finds  that  the  results  are  lower  with  5  grammes  than  when 
10  or  20  are  used.  Where  a  large  amount  of  work  is  being  done 
the  fluxes  are  mixed  together  in  proportions  somewhat  as  follows : 
5  parts  carbonate  of  soda,  7  parts  carbonate  of  potash,  2  parts  flour, 
J  part  borax  glass.  This  mixture  is  kept  in  stock,  a  given  quan- 
tity measured  out  and  placed  in  the  crucible ;  the  ore  is  then  weighed 
out,  thoroughly  mixed  with  it,  and  a  layer  of  salt  placed  on  top, 

A  large  amount  of  soda  or  alkali  is  advisable  owing  to  reaction 
on  page  67,  carbonates  of  the  alkalies  throwing  metallic  lead 
down  from  a  sulphide. 

In  regard  to  the  temperature  used  and  the  time  given  to  th< 
fusion,  some  assayers  recommend  a  short  quick  fusion,  others  a 
long  one,  even  up  to  i^  hours.  It  seems  to  the  writer  that  it  ii. 
more  a  question  of  having  the  temperature  just  right  at  the 
beginning  of  fusion,  during  the  first  15  or  20  minutes,  when  the 
main  bulk  of  the  substance  is  being  decomposed  end  the  lead 
•compounds  reduced  to  metallic  lead,  than  it  is  a  question  of 
length  of  time  of  the  fusion.  The  iron  of  course  must  not  be 
covered  with  globules  of  lead  when  the  fusion  is  poured,  for  this 
is  a  sure  indication  that  it  is  not  complete.  Some  do  not  pour 
the  fusion,  but  allow  it  to  cool  in  the  crucible,  which  when  cold 
is  broken.  This  method  will  often  give  higher  results  than 
when  fusion  is  poured. 

My  reason  for  thinking  it  a  question  of  temperature  at  the 
beginning  is,  that  if  six  or  more  students  are  given  an  ore  carry- 
ing, we  will  say,  82%  of  lead,  and  they  are  all  told  to  use  the 
same  charge  and  fuse  for  50  minutes  in  the  muffle,  some  will 
obtain  81%  to  82%  and  others  only  74%  to  78%;  the  ore,  the 
charge,  and  the  time  being  the  same  in  every  case,  it  stands  to 
reason  the  fault  must  be  with  the  temperature. 

The  smelters  pay  for  90%  of  bad  contents  of  ore,  at  so  much 
per  pound  of  lead,  based  on  the  fire  assay  or  the  wet  analysis, 
less  2%. 


CHAPTER   VI. 
BULLION. 

Bullion. — In  the  Engineering  and  Mining  Journal  of  Febru- 
ary, 26,  1898,  Messrs.  C.  Whitehead  and  T.  Ulke  in  an  article 
"The  Assaying  of  Silver  Bullion,"  say: 

"Silver  bullion,  broadly  speaking,  is  classified  as  follows: 
Dore  bars  are  such  as  contain  gold  and  base  metals  (chiefly 
Cu,  Pb,  often  Sb,  and  sometimes  S),  together  with  from  925  to- 
990  parts  of  silver. 

' '  Fine  silver  bars  are  those  which  are  free  from  gold  and  suffi- 
ciently free  from  alloys  to  render  them  fit  for  coinage  and  for  use 
in  the  arts.  They  average  from  990  to  999  parts  of  silver  per  1000. 

"Base  bars  contain  a  large  percentage  of  base  alloys,  usually 
Pb,  Sb,  or  Cu,  from  100  to  925  parts  of  silver  per  1000,  and  often 
gold. 

"At  the  United  States  mints  and  assay  offices  bullion  con- 
taining less  than  half  its  weight  in  gold  is  classified  as  silver  bul- 
lion, and  the  silver  contained  can  not  be  purchased,  but  must  be 
returned  to  the  depositor  in  the  shape  of  fine  silver  or  merchant's 
bars  (999  fine),  while  both  the  gold  and  silver  in  bullion  with 
50%  and  over  of  gold  (classified  as  gold  bullion)  will  be  paid 
for  by  the  Government.  Except  in  the  case  of  fine  bars,  from 
which  only  cuttings  are  taken,  as  in  the  case  of  gold,  silver  alloys 
are  melted,  thoroughly  stirred,  and  are  then  sampled  in  the  fol- 
lowing way:  One  or  more  portions,  depending  upon  the  weight 
of  the  deposit,  are  dipped  from  the  melting-pot  and  poured  from 
a  height  of  3  feet  in  quantities  of  about  an  ounce,  in  a  fine  streamx 
into  cold  water.  The  resulting  granulations  are  carried  in  cop- 
per cups  to  the  assayer's  laboratory.  However,  in  addition  it 
is  advisable  for  the  assayer  to  take  two  chips  from  silver  bars> 
as  the  chip  and  the  granulation  samples  check  closely  in  gold 

and  near  enough  in  silver  to  identify  the  samples,  should  a** 

198 


BULLION.  199 

interchange  of  melts  have  occurred.  After  drying  the  granu- 
lations by  heat,  about  1-5  ounces  is  reserved  in  the  assay 
room  and  the  remainder  returned.  The  sample  lots  are  now 
laid  out  upon  a  board  containing  cup-like  sockets  bored  at  regu- 
lar intervals  and  numbered.  A  granulation  from  each  sam- 
ple is  next  hammered  and  rolled  into  a  thin  strip,  this  being 
merely  for  convenience  in  cutting  for  the  adjustment  in  weigh- 
ing the  assay.  Each  strip  is  laid  beside  its  kindred  granulations 
and  numbered  by  stamping.  The  board  is  now  removed  to 
the  assayer's  weigh- room." 

The  'silver  is  determined  by  the  volumetric  or  Gay-Lussac 
assay,  a  full  description  of  which  will  be  found  in  the  above 
article. 

Lead  Bullion  or  Base  Bullion. — This  may  be  lead  carrying 
either  silver  or  gold  or  both  silver  and  gold,  but  it  is  seldom  as 
pure  as  this  and  generally  contains  Cu,  As,  Sb,  Zn,  and  similar 
impurities. 

The  bullion  may  be  in  bars  or  in  the  condition  of  borings  or 
of  cuttings.  Samples  for  assay  

,     ,  r  ,1         U  •  (      o     o     o     o    )  C*      n      "      „       "~) 

are  taken  from  the  bars  or  pigs 

by  sawing,  cutting,  punching,  or  boring  them. 

Dip  samples,  taken  when  the  bullion  is  melted,  or  those  taken 
by  sawing,  are  the  most  accurate.  Never  cut  samples  off  the  cor- 
ners of  a  bar.  Composition  of  the  same  pig  varies  in  places. 
G.  M.  Roberts,  in  Trans.  A.I.M.E.,  shows  that  samples  taken 
from  side  of  moulds  or  ingots  may  be  richer  than  the  rest  of  ingots. 

Preliminary  Test. — To  determine  if  the  bullion  can  be  cupelled 
directly,  take  i  gramme  or  so  (do  not  weigh  it)  and  either  wrap 
it  in  C.P.  lead  or  drop  it  as  it  is  into  a  hot  cupel.  If  impurities 
like  Cu,  Sb,  As,  Sn,  etc.,  are  present  in  considerable  quantity, 
the  bullion  will  not  drive,  or  else  will  drive  and  then  freeze  after 
a  short  time. 

Regular  Assay. — If  the  bullion  will  not  cupel,  take  two  or 
three  portions  of  J  A.T.  each,  scorify  with  an  additional  amount  of 
lead  (30  to  45  grammes),  and  then  cupel. 

Bullion  containing  tin  often  gives  trouble;  therefore  if  J  A.T. 
of  it  will  not  scorify  with  an  additional  45  grammes  of  lead  and 
some  borax  glass ,  decrease  the  amount  of  bullion  and  increase 


NOTES  ON  ASSAYING. 

the  amount  of  lead  and  borax  glass,  and  continue  to  do  this  until 
it  scorifies  satisfactorily.  It  is  simply  a  question  of  more  lead  and 
borax  glass,  provided  the  heat  is  sufficiently  high. 

If  the  bullion  cupels,  weigh  out  carefully  two  or  three  portions 
of  J  A.T.  each,  and  be  sure  that  each  contains  the  same  propor- 
tion of  coarse  and  fine  drillings  as  are  contained  in  the  bullion 
sample.  Take  two  or  three  pieces  of  C.P.  sheet  lead  which  weigh 
the  same,  and  wrap  each  lot  of  bullion  in  a  piece  of  lead  so  that 
.the  whole  is  very  close  and  compact.  This  should  be  done  in  a 
scorifier:  in  case  the  lead  wrapping  breaks,  any  bullion  coming 
out  will  be  saved.  If  the  lump  is  not  compact,  it  may  overflow  the 
cupel  while  melting,  or  else  leave  small  particles  on  the  sides  of 
the  cupel,  whch  will  not  come  down  into  the  main  button. 

Keep  the  heat  so  low  that  feather  crystals  of  PbO  will  always 
jorm.  Have  two  or  three  hot  cupels  in  the  muffle  to  cover  the 
others  with  as  soon  as  the  blick  occurs.  Have  the  buttons  solidify 
•as  quickly  as  possible  to  avoid  loss  of  Ag,  and  withdraw  from  the 
furnace  slowly  to  avoid  sprouting. 

Sprouted  buttons  should  be  rejected. 

Bullion  up  to  400  oz.  should  check  within  J  oz.  for  total  Ag 
and  Au. 

The  buttons  are  cleaned,  hammered,  or  rolled  out,  weighed, 
and  parted  as  described  under  Assay  of  Gold  Ores. 

Report  results  in  ounces  per  ton  for  both  Ag  and  Au  in  bul- 
lion under  500,  i.e.,  carrying  less  than  50%  of  both  metals. 

Experiment. — Take  or  cut  off  from  the  bullion  given  to  you 
about  35  grammes.  If  not  fine  or  in  small  pieces,  cut  it  up  and 
mix  thoroughly.  Make  the  preliminary  test  as  per  page  199. 
If  the  button  does  not  cupel,  take  two  portions  of  £  A.T.  each 
and  scorify  with  40  or  more  grammes  of  granulated  lead.  If 
this  does  not  scorify,  use  less  bullion,  more  lead,  and  some  borax 
glass.  Then  cupel  as  directed. 

If  the  bullion  taken  for  preliminary  test  cupels  and  button 
blicks,  then  weigh  out  accurately  on  the  pulp-balances  two  por- 
tions of  \  A.T.  each. 

Weigh  out  two  portions  of  C.  P.  sheet  lead  from  10  to  15 
grammes  each  and  have  them  balance  each  other.  Wrap  the 
^bullion  up  very  tightly  in  these. 


BULLION.  201 

Have  the  cupels  hot  and  drop  the  bullion  into  them,  and 
cupel  with  feather  litharge  crystals.  When  buttons  blick,  cover 
with  hot  old  cupels,  which  have  been  heating  in  the  back  of 
muffle,  and  withdraw  slowly  from  furnace. 

Clean  and  weigh  the  silver  and  gold  beads.     Part  for  gold. 

Report  the  following: 

1.  Weight  of  C.P.  lead  used. 

2.  Time  of  cupellation. 

3.  Amount  of  lead  oxidized  per  minute,  including  lead  in  bul- 
lion taken. 

4.  Ounces  per  ton  in  gold. 

5.  "       "      "    "  silver. 

Silver  Bullion  containing  no  Gold. — Silver  and  gold  bullion 
are  reported,  not  in  ounces  per  ton,  but  in  fineness  or  parts  in 
a  thousand.  That  is,  if  the  bar  of  bullion  carries  95%  of  silver 
and  5%  of  gold,  we  say  it  is  950  fine  in  silver  and  50  fine  in  gold. 

The  best  three  methods  for  determining  the  silver  contents  are : 

ist.  Fire  assay.     Cupellation  with  C.P.  lead. 

2d.  Volumetrically,  with  a  standard  solution  of  salt. 

3d.  Volumetrically,  with  a  standard  solution  of  sulphocy- 
anide  of  potash  (German  method). 

The  first  and  second  methods  require  a  preliminary  assay  to 
determine  the  approximate  fineness  of  the  bullion  to  be  assayed. 

Preliminary  Assay. — Calculate  as  per  pages  203  and  204,  see 
also  page  205.  On  the  fine  button-balance  weigh  out  .5000  grammes 
of  the  bullion,  wrap  it  in  about  5  grammes  C.P.  lead-foil  and 
cupel  carefully,  keeping  the  heat  low  enough  to  form  the  litharge 
crystals,  but  not  so  low  as  to  freeze  the  button.  Take  the  button 
from  the  cupel,  clean,  hammer,  and  weigh  it  carefully  in  the 
usual  manner.  Part  the  button  to  see  whether  there  is  any  gold 
in  it,  and  then  calculate  the  approximate,  fineness  of  the  bullion. 

The  whole  object  of  the  work,  thus  far,  is  to  ascertain  the 
approximate  composition  of  the  bullion;  having  done  this,  the 
''check  assay"  can  be  made  to  correspond,  so  that  if  it  is  found 
that  there  are  .475  grammes  of  silver  in  .500  grammes  of  bullion, 
weigh  out  .4800  grammes  of  C.P.  silver,  wrap  it  up  in  5  grammes 
C.P.  lead-foil  and  cupel  by  the  side  of  the  regular  assay.  We 
weigh  out  .480  grammes  in  this  case  because  fine  bullion  gener- 


202  NOTES   ON  ASSAYING. 

ally  loses  between  4  and  5  milligrammes  when  .500  grammes  of 
bullion  are  used. 

Whatever  the  percentage  loss  of  silver  the  "check"  or  "proof 
assay"  shows  it  is  fair  to  assume  that  the  bullion  being  assayed  also- 
sustains. 

For  this  reason  I  prefer  to  figure  the  percentage  loss  and 
make  up  the  check  as  per  the  examples  given  on  pages  203  and 
204,  rather  than  work  by  the  table  on  page  207,  taken  from  Van 
Furman's  Manual  of  Practical  Assaying. 

From  his  table  the  amount  of  C.P.  silver-  foil  can  be  figured 
that  it  will  be  necessary  to  use  in  the  check  assay,  if  the  work 
is  being  done  by  the  first  method,  and  the  amount  of  bullion  to 
use  if  the  second  method  is  employed. 

Actual  Assay.  —  Calculate  as  per  pages  203  and  205. 

Weigh  out  as  accurately  as  possible  two  portions  of  the  bullion, 
say  .49900  and  .49980  grammes.  Wrap  each  just  as  compactly  as 
possible  in  5  grammes  C.P.  lead-foil,  so  the  bullion  will  not  spread 
in  the  cupel.  Make  up  the  proof  or  "  check  "  as  shown  by  the 
preliminary  assay,  weighing  it  out  just  as  accurately  as  the  bullion, 
and  wrapping  it  in  exactly  the  same  amount  of  C.P.  lead-foil  as 
was  used  with  the  two  samples  of  bullion  to  be  valued. 

Have  three  cupels  heated  hot,  side  by  side  in  the  muffle,  and 
then  drop  the  three  buttons  quickly  into  them,  placing  the  check 
in  the  middle  one.  Close  the  door  of  the  muffle,  that  the  buttons. 


Bullion  Check  Bullion 


may  "  drive  "  as  soon  as  possible  and  all  at  once.  When  they  are 
"driving,"  open  the  door  immediately  and  cupel  them  at  as  low 
a  temperature  as  possible  without  freezing,  always  obtaining  the 
leather  litharge  crystals;  push  back  into  muffle  just  before  blick- 
ing.  Endeavor  to  have  them  "blick"  together,  and  then  draw  out 
slightly  toward  the  front  of  the  muffle  until  they  chill.  Just  as 
soon  as  they  have  done  so,  cover  them  over  with  hot  cupels  or  hot 
'scunners,  which  should  have  been  heating  in  the  muffle;  with- 
draw slowly  from  the  furnace  to  avoid  sprouting,  cool,  hammer,. 


BULLION. 


203 


clean,  weigh,   and   part  for  gold.     In  bullion  containing  gold  all 
three  buttons  have  to  be  parted  (see  page  206) . 

EXAMPLE  No.  i. — Preliminary  Assay.  (To  determine  the  ap- 
proximate fineness  of  the  bullion.) 

Take,  for  instance,                                   -49909  gms.  of  bullion. 
Silver  found  after  cupellation,  i.e.,  the 
bullion  was  wrapped  in  C.P.  lead 
and  cupelled 49144  gms.,  or  98.47% 

Loss  =  .00765  grammes. 

The  amount  of  silver  in  this  loss  is  probably  .00500  ±  grammes, 
and  the  remainder  impurities  in  the  bullion. 

Actual  Assay.  (To  determine  actual  fineness  of  bullion). — 
Weigh  out  accurately  two  samples  of  the  above  bullion. 

Suppose  they  weigh  as  follows: 

Sample  No.  i.  Sample  No.  2. 

.  49900  grammes.  .49980  grammes. 

Average  =  .49940  grammes. 

To  determine  the  amount  of  silver  to  weigh  out  for  the 
check,  take 


Preliminary 
assay. 

.49909 


Average  of 

2  samples 

taken. 

.49940 


Ag.  found  in 
preliminary. 

.49144 

.00500   ±    Supposed  loss. 


Silver  for 
check. 

#=.49674 


.49644 

The  two  samples  of  bullion  and  the  "  check  "  are  wrapped  in. 
pieces  of  C.P.  sheet  lead,  all  of  the  same  weight  (six  or  more 
grammes) ,  and  cupelled. 


No.  i  sample  .  . 
After  cupelling. 

.'.  99.11%  :  ioo 


.49900         Check  (C.P.  Ag)  .    .49^74 
.49152         After  cupelling ...    .49230 


No.  2  sample. . 
After  cupelling.. 

loss  of  silver. 


.00444= 

.49152  silver  found  in  sample  :  #  (silver  in  sample  if  there 
No.  i  had  been  no  loss  of  silver) 


#=.49593; 


•49593. 
.49900" 


=  99.38%  or  993.85  fine. 


Sample  No.  2  is  calculated  in  the  same  way. 


204 


NOTES  ON  ASSAYING. 


EXAMPLE  No.  2. — Preliminary  Assay. — Bullion  taken  =  .5000 
grammes.  -Silver  found  =.2500  grammes. 

Suppose  the  loss  of  silver  =  . 00500  ±  grammes. 

Then  the  silver  in  the  bullion  is  probably  .  255  ±  grammes 
and  the  impurities   "     "       "       are      "         .245±         " 

Actual  Assay. 

Bullion  No.  i.  Bullion  No.  2. 

.5000  grammes.  .48000  grammes. 

Average  =  .  49000  grammes.   • 

Therefore  .5000  :  .4900  ::  .2550  :  #=  .2499  grammes. 

C.P.  silver-foil  to  be  weighed  out  for  "  check  "  = ,  2499  grammes. 

Impurities  like  copper  materially  affect  the  loss  of  silver,  and 
as  we  wish  to  have  the  "  check  "  correspond  as  nearly  as  possible 
to  the  bullion,  a  like  amount  of  copper  is  to  be  added  to  the 
""check."  This  bullion  should  be  wrapped  in  15  to  20  grammes  of 
C.P.  lead. 

In  Mitchell's  Assaying  (page  628)  is  found  the  following 
table  in  regard  to  an  alloy  of  silver  and  copper: 


Standard 
of 
Silver. 

Quantity  of 
Copper  Alloyed. 

Amount  of  Lead  Necessary 
to  Add. 

Relation  of  Lead 
to  Copper. 

IOOO 

0 

3/10  grammes   or  as  small 

an  amount  as  possible 

— 

95° 

50 

3  grammes 

60  to 

900 

TOO 

7        " 

70  to 

800 

2OO 

10 

5°  to 

700 

300 

12 

40  to 

600 

400 

14 

35  to 

500 

500 

1  6  to  17  grammes 

32  to 

400 

600 

16  to  17         " 

27  to 

300 

700 

16  to  17         " 

23  to 

2OO 

800 

16  to  17         " 

20  to 

100 

QOO 

16  to  17         " 

18  to 

"  Long  experience  has  proved  that  silver  opposes  the  oxidation 
of  copper  by  its  affinity,  so  that  it  is  necessary  to  add  a  larger 
amount  of  lead  in  proportion  to  the  quantity  of  silver  present." 

Sufficient  lead  must  be  added  to  cause  the  button  to  unite 
well.  If  too  great  an  excess  is  used,  however,  the  loss  of  silver  will 
be  large,  owing  to  the  duration  of  the  cupelling  process.  Some 
assayers  prefer  to  add  the  lead  to  the  cupels  at  first,  have  it 


BULLION.  203 

driving  well  and  then  drop  the  sample  of  bullion,  wrapped  in 
thin  C.P.  sheet  lead,  into  the  lead  which  is  already  driving. 

As  has  been  previously  shown,  if  the  cupels  used  in  the  bullion 
assays  and  check  are  saved,  pulverized,  and  assayed  by  the  cru- 
cible method,  about  90%  of  the  silver  found  to  have  been  lost 
will  be  recovered  from  the  cupel.  This  shows  that  the  loss 
sustained  during  cupellation  is  largely  due  to  absorption.  The 
remainder  of  the  loss  can  be  accounted  for  by  volatilization. 

Some  experiments  seem  to  show  that  5  parts  of  lead  are 
required  to  cupel  an  alloy  of  900  Ag  and  100  Cu  in  the  middle 
of  the  muffle,  10  parts  in  the  front,  and  3  parts  in  the  back;  i.e., 
the  higher  the  heat  the  less  lead  is  required. 

Silver  Bullion  containing  Gold.  —  Preliminary  Assay.  (To 
determine  the  approximate  fineness  of  the  bullion.) — Weigh  out, 
say,  .49850  grammes  of  bullion,  wrap  it  in  from  3  to  5  grammes 
of  C.P.  lead-foil  and  cupel. 

After  cupelling,  button  weighs ....  49000      grammes  * 

Probable  loss  in  Ag 00500  ± 

(Gold  loss  is  supposed  to  be  very 

small.) 
Impurities 00350  ±        " 

.49850  ± 

That  is  to  say,  the  silver  in  the  bullion,  originally  taken,  is 
probably  .  48500  ±  grammes. 

Actual  Assay.  (To  determine  actual  fineness  of  bullion.) — 
Weigh  out,  for  example,  .  49860  and  .  49880  grammes  of  bullion, 
The  average  =  .49870  grammes. 

Then  the  silver  in  the  check  will  be 

Prelim.  Av.  of  two         Ag  probably 

bullion.  samples.  in  prelim. 

.49850   :    .49870   ::    .4850   :   #=.48519 
The  gold  will  be 

.49850  :    .49870   ::    .0100  :   #=.0100 


Au  =  .oioo 

.4900  grammes 


2.o6  NOTES   ON  ASSAYING. 

We  now  have 
Sample  No.  i.  Check.  Sample  No.  2. 

.49860        C.P.  Ag  foil 48519         .49880  grammes 

Au     from     parting 
preliminary oiooo 

Wrap  them  in  three  pieces  of  C.P.  lead-foil  which  balance 
<each  other;  4  to  6  grammes  will  probably  be  enough,  but  it  must 
be  sufficient  to  bring  the  bullion  all  into  one  globule,  when  melted. 

After  cupelling : 

Sample  No.  i.  Check.  '        Sample  No.  2. 

Ag+Au 49°°5  -49OI5  -49032 

Au  from  parting oiooo  .00996  .01002 


Ag 48005  . 48019  . 48030 

Ag  lost  in  cupelling , 00500 

Au    "    "         "       00004 

Percentage  Ag  lost -1— - — =1.03 

.48519 

Therefore  .48005  (Ag  found  in  sample  No.  i)  must  equal 
98.97%. 

Therefore  98.97   :   100  ::    .48005   :   #=.48505 

Fineness  of  No.  i  in  silver  =       ^  5  =072.82 

.49860 

Percentage  Au  lost  ( )  =  .4 

\. oiooo/ 

Therefore  99.6   :   100  ::    .oiooo   :  ^=.01004 

<•  -XT  11      .01004 

Fineness  of  No.  i  in  gold  = -—^  =  20.13 

. 49860 

Impurities  =.7% 

The  fineness  of  sample  No.  2  is  calculated  in  the  same  way. 

Loss  of  Silver  in  Bullion  containing  Gold. — The  following 
results,  taken  at  random,  will  give  an  idea  of  the  losses  found 
by  students  when  assaying  bullion. 

Bullion  taken  varied  from  .4500  to  .5040  grammes.  Lead 
used,  3  to  6  grammes. 


BULLION, 


207 


Fineness 
in  Silver. 


800+ 
972+ 

923+ 
998 

974+ 
969+ 
996 


Fineness 
in  Gold. 

50+ 

22  + 

39+ 

2 

20+ 
25+ 
3-51 


Total  Loss  of  Silver,  i  e. 

by  Volatilization  and 

Absorption  by  Cupel. 

in  Per  Cent 


.60 
1.09 

•78 
.78 
.90 


Wet  Methods. — When  the  Gay-Lussac  method  with  salt  or 
the  sulphocyanide  method  are  employed,  the  bullion  is  often 
.assayed  by  fire  to  determine  its  approximate  fineness.  The  fol- 
lowing table  is  taken  from  Furman's  Practical  Assaying. 


If  preliminary  assay  of 
.500  grammes  gives 

The  silver  to  be  used 
in  check  is 

C.P  Lead. 

Bullion  to  be  used 
in  Second  Method. 

.  4900  grammes  Ag 

.49500  grammes 

5  grammes 

.4800 

" 

.  48500        ' 

5 

•475° 

.480 

5 

.042  grammes 

.4500 

.455  to  .460  * 

7 

.091 

,4250 

.430  to  .435  * 

8 

.156 

.400 

.405  to  .410  ' 

10 

.  227 

-375 

.38010  .385  ' 

ii 

•307 

-35° 

.355  to  .360  ' 

12 

•399 

-325 

•330  to  .335  ' 

1.3 

5°4 

.300 

.305  to  .310  ' 

15 

.610 

.250 

.255  to  .260  ' 

17 

.922 

.200 

.205  to  .210  ' 

19 

2.380 

•150 

.  155  to  .  160  ' 

20 

3-125 

Silver  Bullion.  Volhard's  Wet  Method. — This  method  depends 
upon  the  total  precipitation  of  the  silver  in  a  strongly  acid  solution 
(HNO3)  by  means  of  a  standard  solution  of  potassium  sulphocy- 
anide (KCyS)  or  ammonium  sulphocyanide  (NH4CyS).  The  end 
point  is  shown  by  the  supernatant  clear  liquid  becoming  a  per- 
manent reddish-brown  color  (ferric  sulphocyanide),  when  a  solu- 
tion of  ferric  alum  or  ferric  sulphate  is  added  to  the  silver  solu- 
tion as  an  indicator. 

The  solution  of  KCyS  can  be  made  up  in  either  of  two  ways, 

First.    From   the   reaction  AgNO3+KCyS  =  AgCyS  +  KNO, 

we  find  that  97.17  parts  of  KCyS  will  precipitate  107.93  parts 

of  Ag.    It  follows  that  i  gramme  of  Ag  will  require  .9003  grammes 

of  KCyS.    Now  it  has  been  found  convenient  to  make  the  KCyS 


208  NOTES  ON  ASSAYING. 

solution  of  such  strength  that  i  c.c.  will  equal  10  milligrammes 
of  Ag. 

If,  therefore,  we  dissolve  9.003  grammes  of  KCyS  in  H2O  and 
make  the  solution  up  to  1000  c.c.,  each  c.c.  of  solution  will, 
according  to  the  reaction,  represent  10  milligrammes  of  Ag. 

The  KCyS  is,  however,  very  deliquescent,  and  it  is  difficult 
to  weigh  it  out  accurately  -t  therefore  the  best  way  to  do  is  to 
have  a  No,  i  beaker  and  weigh  into  it  a  little  over  9  grammes 
of  KCyS,  (dissolve  this  in  distilled  H2O,  filter  if  necessary,  and 
make  up  to  i  litre. 

The  indicator  may  be  either  a  10%  solution  of  ferric  sulphate 
or,  better,  a  saturated  solution  of  ferric  ammonium  sulphate 
(ferric  alum).  Make  up  about  100  c.c.  of  either;  next  weigh  out 
two  portions  of  C.P.  silver  of  about  .5  grammes  each.  Dissolve 
in  50  c.c.  of  HNO3  (sp.  gr.  1.2)  and  boil  to  drive  off  nitrous  fumes. 
Dilute  with  H2O  to  200  c.c.,  allow  it  to  get  perfectly  cold,  and 
add  about  5  c.c.  of  the  indicator  solution.  Titrate  and  stir  con- 
stantly. The  end-point  is  a  permanent  light  reddish-brown 
color,  and  the  supernatant  liquid  should  show  no  cloudiness. 

The  KCyS  solution  will  probably  be  too  strong,  more  than 
9  grammes  of  the  salt  having  been  weighed  out.  It  is  an  easy 
matter  now  to  calculate  the  amount  of  H2O  which  must  be  added 
to  the  KCyS  solution  in  order  to  make  i  c.c.  of  this  solution 
equal  to  10  milligrammes  of  silver. 

After  having  added  the  necessary  amount  of  water,  titrate 
the  second  C.P.  silver  solution.  The  KCyS  ought  now  to  be  of 
such  strength  that  each  c.c.  is  exactly  equal  to  10  milligrammes 
of  silver.  If  this  is  not  the  case,  the  necessary  correction  should 
be  made  from  the  second  titration  and  either  water  or  a  few  crys- 
tals of  KCyS  added  to  the  solution.  Titrate  again. 

Second  Method  for  making  up  the  KCyS. — Weigh  out  a  little 
over  9  grammes  of  the  salt  and  make  up  to  i  litre.  Next  weigh 
out  accurately  three  or  more  portions  of  C.P.  silver  of  about 
J  gramme  each  and  titrate  each  of  the  solutions.  They  should 
agree  very  closely,  and  from  them  the  value  in  silver  of  each 
c.c.  of  KCyS  is  calculated. 

Bullion   Analysts. — If    one    prefer    to    take    large    amounts, 


BULLION.  209 

weigh  out  accurately  two  or  more  portions  of  i  to  2  grammes 
each  and  titrate  them  separately;  or  weigh  out  i  gramme  or 
over,  dissolve  in  100  c.c.  HNO3  (sp.  gr.  1.20)  or  30  c.c.  of  strong 
acid  (sp.  gr.  1.42),  boil  to  drive  off  nitrous  fumes,  and  make  up 
to  500  c.c.  in  a  graduated  flask.  Shake  the  flask  well,  take  out 
portions  of  200  c.c.  each  and  titrate.  The  results  should  agree 
within  .05  c.c. 

The  best  method,  however,  seems  to  be  to  weigh  out  as  closely 
as  possible  two  or  more  portions  of  J  gramme  each,  dissolve  in 
10  c.c.  of  HNO3,  boil  until  nitrous  fumes  are  driven  off,  cool,  and 
add  50  c.c.  of  water  and  5  c.c.  of  the  indicator  solution.  Titrate 
as  usual.  The  solutions  must  be  COLD  and  entirely  free  from 
nitrous  fumes,  and  the  amount  of  indicator  added  must  be  the 
same  in  each  case. 

The  KCyS  does  not  change  if  kept  cool  and  away  from  the 
sunlight.  If  upon  titrating,  the  red  color  disappears,  it  is  prob- 
ably due  to  the  presence  of  nitrous  acid  or  AgCl.  Nitrous  fumes 
and  HNO3  destroy  the  color  in  hot  solutions.  Copper  may  be 
present  up  to  70%  and  not  interfere  with  the  titration.  Beyond 
this  amount,  the  copper  sulphocyanide  thrown  down  obscures  the 
end-point.  Cuprous  sulphocyanide  is  insoluble  in  the  solution. 
Cupric  sulphocyanide  is  soluble  in  the  solution.  Pb,  Cd,  Bi, 
Zn,  Fe,  Mn,  As,  Sb,  Sn,  and  Th  do  not  interfere  with  the  titra- 
tion. Hg,  Co,  Ni,  Cl,  and  palladium  interfere  with  it. 

Results  should  agree  to  within  .5  at  least;  that  is,  if  one  comes 
988.5,  the  other  should  not  be  lower  than  988. 

Recovery  of  Silver  from  Solutions. — All  the  silver  nitrate  and 
silver  sulphate  solutions  from  parting,  as  well  as  all  the  solutions 
and  residues  from  volumetric  work,  should  be  saved  and  the  silver 
recovered. 

From  Silver  Nitrate. — When  HC1  or  a  soluble  chloride  is 
added  to  any  soluble  salt  of  silver,  except  the  hyposulphite,  a 
precipitate  will  be  thrown  down. 

This  precipitate  is  soluble  in  NH4OH,  sodium  hyposulphite, 
sodium  chloride,  potassium  cyanide,  tartaric  acid,  and  soluble 
sulphites.  .  Owing  to  its  solubility  in  a  strong  brine,  HC1  seems 
a  more  suitable  precipitant  than  salt. 


210  NOTES  ON  ASSAYING. 

Have  the  solution  boiling  before  adding  the  precipitant,  and 
-after  adding  it  stir  well  until  the  AgCl  collects  in  lumps,  settles, 
and  leaves  a  clear  supernatant  liquid.  Filter  and  wash  thor- 
oughly with  hot  water  by  decantation. 

The  silver  may  be  recovered  from  the  AgCl  in  several  ways; 
among  the  best  are  the  following: 

1.  Place  the  AgCl  in  a  vessel,  cover  with  water,  add.  strips 
of  zinc  and  sufficient  H2SO4  or  HC1  to  start  action  on  the  zinc: 

Zn+H2SO4  =  ZnSO4+  2H; 
2H+2AgCl=2Ag+2HCL 

When  the  AgCl  has  all  been  changed  to  metallic  silver,  indi- 
•cated  by  its  dark  appearance,  wash  with  hot  water  until  free 
fi;om  zinc  salts,  filter,  and  melt  in  a  graphite  crucible. 

2.  Fuse  the  AgCl  with  sodium  carbonate: 

2AgCl+Na2CO3=2Ag+2NaCl+CO2+O. 

3.  Mohr's  Method. — Mix  the  dry  AgCl  with  1/3  its  weight  of 
resin  and  fuse  in  a  crucible  glazed  on  the  inside  or  a  graphite  one. 
'The  hydrogen  reduces  the  AgCl  to  Ag. 

Organic  matter,  cane  and  grape  sugar  also  decompose  the 
AgCl  with  a  reduction  of  metallic  silver. 

4.  4  AgCl+2CaO  +  C  =  4Ag+2CaCl2+CO2. 

From  AgCyS. — Filter  the  solutions,  wash  and  dry  the  AgCyS. 
Mix  with  ten  times  its  weight  of  sodium  carbonate,  and  fuse  with 
a  little  borax  in  a  crucible  glazed  on  the  inside. 

It  is  necessary  to  use  a  very  large  excess  of  soda,  otherwise  a 
silver  matte  (Ag2S)  will  be  formed  besides  the  silver  button.  The 
reaction  is  probably  as  follows: 

2AgCyS+  3Na2CO3=  2Ag+  2NaCy+  2Na2S+  3CO2+  30. 

Gold  Bullion.* — Experiments  at  the  mints  seem  to  show  that 
the  amount  of  gold  lost  in  cupellation  increases  with  the  amount 
of  lead  used,  and  decreases  as  the  silver  in  the  alloy  increases.  For 
-this  reason,  as  in  the  assay  of  silver  bullion,  we  aim  to  use  the 

*  Mitchell's  Assaying. 

T.  K.  Rose,  Limits  of  Accuracy  of  Bullion  Assay. 
Eng.  and  Mining  Journal,  Feb.  12,  1898. 


BULLION. 


211 


smallest  amount  of  lead  that  will  oxidize  and  get  rid  of  the  impuri- 
ties in  the  bullion,  and  which,  at  the  same  time,  will  collect  the 
sample  or  drillings  in  a  good  button  when  the  assays  first  begin 
to  drive.  Copper  also  influences  the  loss  and  seems  to  have 
a  greater  affinity  for  gold  than  it  has  for  silver. 

When  the  bullion  contains  this  metal  add  i\  to  3  times  as 
much  silver  as  gold  and  use  the  following  proportions  of .  lead 
(Mitchell's  Assaying,  page  759) : 


Gold, 
Parts  in  1000. 

Copper, 
Parts  in  1000. 

Amount  of  Lead  required  when 
i  Gramme  of  Bullion  is  used. 

IOOO 
900 
800 

O 
IOO 
200 

i  par     ,     j  gramme  aiiOy 
^H  10  grammes  lead 

700 

300 

22         ' 

600 

400 

24         ' 

500 

500 

26         ' 

400  to  100 

34       ' 

The  assay  is  made  practically  in  the  same  way  as  in  the  silver 
bullion.  First  we  make  a  preliminary  assay  to  determine  the 
approximate  fineness.  Weigh  out,  say,  .5000  grammes,  also  2j  to 
.3  times  as  much  (C.P.)  Ag,  and  wrap  in  some  (C.P.)  Pb.  Cupel 
•at  as  low  a  temperature  as  possible  (feather  litharge  crystals), 
remembering  that  towards  the  end  we  must  have  a  slightly  higher 
temperature  than  in  the  silver  bullion,  to  insure  a  good  "blick." 
Gold  melts  at  1064°  C.  and  silver  at  961.5°  C.  Clean  the  but- 
ton carefully  and  weigh. 

Anneal  button,  hammer,  anneal  again,  hammer,  and  finally 
•either  hammer  flat  or  else  roll  out  into  a  thin  strip.  Part  in 
the  usual  manner  in  HNO3  and  weigh  the  resulting  gold. 

Suppose  our  preliminary  assay  shows: 

.  39000  grammes  of  gold  =  78%  or  780  fine. 

.010  of  silver  =   2%  or    20     " 

.100  loss  and  impurities 

(for  instance,  copper)  =  20% 

From  this  we  can  make  up  our  check,  which  should  corre- 
spond to  the  bullion  as  nearly  as  possible.  That  is,  if  we  take 

.  5000  grammes  of  bullion, 
i .  1900        ' '        of  C.P.  silver  (.395  X  3), 


212  NOTES  ON  ASSAYING. 

and  wrap  in  8  to  10  grammes  of  C.P.  lead-foil  (780  fine;   .*.  the 
Pb=i6X-5,  page  211);  our  check  should  consist  of 

.39500  grammes  C.P.  gold       (This  is  supposing  that  J  gramme 

of  gold  loses  about  .005  during 
cupellation.) 
1.2000          "        C.P.   silver  (1.19 +.010  in  the  bullion.) 

.0950          "        C.P.  copper 

Weigh  out  two  portions  of  the  bullion  and  wrap  each  in  8 
grammes  of  C.P.  lead.  Drop  all  three  buttons  into  three  hot 
cupels  and  conduct  the  cupellation  so  as  to  have  feather  litharge 
crystals.  Weigh  all  three  buttons  carefully  and  part  the  check 
as  well  as  the  other  buttons.  Calculate  the  results  as  per  pages 
203  and  205. 

Report  the  results  in  fineness  to  second  place  of  decimals  as 
in  the  silver  bullion.  For  instance,  993.63  fine. 

If  we  wish  to  determine  the  silver  in  the  bullion  also,  especially 
where  it  is  present  in  very  small  amount,  we  shall  have  to  use  one 
of  the  wet  methods.  See  also  article  by  Mr.  Cabell  Whitehead, 
Chemical  Section,  Franklin  Institute,  Sept.  15,  1891,  "Use  of 
Cadmium  for  Assaying  Gold  Bullion." 

At  the  mints,  after  the  approximate  fineness  is  obtained,  just 
the  right  amount  of  silver  is  added  to  the  gold,  both  are  wrapped 
in  C.P.  lead  and  cupelled.  The  resulting  button  is  rolled  out 
thin,  coiled  into  a  roll,  and  placed  in  a  small  platinum  capsule 
having  openings  in  it.  A  dozen  or  more  of  these  capsules  are 
held  in  a  platinum  tray,  which  is  then  immersed  in  HNO3. 
Three  strengths  of  acid  are  used  in  parting — 1.12,  1.18,  and 
1.27 — and  each  boiling  occupies  5  to  10  minutes.  The  washing 
with  water  is  performed  in  the  same  trays,  which  are  finally  heated 
in  a  muffle.  Each  Pt  capsule  should  contain  a  little  roll  of  gold* 


CHAPTER  VII. 
ASSAY  OF    ORES   FOR    COPPER   AND    TIN. 

COPPER    ASSAY. 

COPPER  melts  at  1084°  C.  Sp.  gr.  8.8  to  8.9.  Atomic 
weight  63.5.  Copper  determinations  can,  of  course,  be  -made 
most  accurately  by  some  one  of  the  wet  methods;  still,  when  the 
ores  are  of  quite  a  uniform  grade,  or  where  the  analysis  or 
character  of  the  gangue  is  fairly  well  known,  very  satisfactory 
results  can  be  obtained  by  the  fire  assay.  It  is  especially  adapted 
to  places  where  laboratory  conditions  are  poor  and  chemicals 
are  not  at  hand.  In  the  Lake  Superior  region,  where  the  cop- 
per exists  in  the  rock  in  a  native  condition,  the  assays  of  the 
products  from  the  mills,  many  of  which  run  over  60%  copper, 
are  made  by  the  fire  assay,  and  the  results  not  only  check  closely, 
but  are  nearer  the  true  value  of  the  material  than  those  obtained 
by  wet  analysis,  because  a  much  larger  amount  of  the  sample 
(50  to  TOO  grammes)  can  be  used  for  a  determination. 

Copper  ores  may  be  divided  as  follows  : 

i.  Sulphide  Ores. 
Chalcopyrite,     Cu2S,Fe2S3  (sp.  gr.  4.1  to  4.3).     01  =  34^%,     Fe 


Erubescite,  or  Bornite,  purple  ore,  3Cu2,S,Fe2S3  (sp.  gr.  4.9  to  5.4)* 

Cu  =  55i%,  8  =  28.1%. 

Chalcocite,  Cu2S  (sp.  gr.  5.5  to  5.8).     01  =  79.8%. 
Covellite,  indigo  copper,  CuS  (sp.  gr.  4.59  to  4.64).  Cu  =  66-4%. 

(Due  to  the  weathering  and  alteration  of  chalcocite.) 
Enargite,  3Cu2S,As2S5  (sp.  gr.  4.43  to  4.51).     01  =  48.3%. 

These  ores  are  of  course  seldom  free  from  iron  pyrites  or 
other  sulphides,  and  they  may  be  also  associated  with  arsenical 

and  antimonial  minerals  and  compounds. 

213 


2T4  NOTES  ON  ASSAYING. 

2.  Oxide  and  Carbonate  Ores. 

Cuprite,  red  oxide,  Cu2O  (sp.  gr.  5.85  to  6.15).     Cu  =  88.8%. 
Tenorite,  or  Melaconite,  black  oxide,  CuO  (sp.  gr.  5.82  to  6.2). 

Cu=79.8%. 
Malachite,  green  carbonate,  CuCO3,Cu(OH)2  (sp.  gr.  3.9  to  4.03). 

01=57.46%. 
Azurite,  blue  carbonate,  2CuCO3.Cu(OH)2  (sp.  gr.  3.77  to  3.83). 

Cu  =  55.29%. 
Chrysocolla,    silicate,    CuSiO3+2H2O    (sp.  gr.  2  to   2.23).     Cu 

=  36.18%. 

3.  Native  Copper  Ores. 

Before  making  the  fusion,  the  ore  to  be  tested  must  be  in  the 
condition  of  either  Class  2  or  3,  for  if  sulphides,  sulphates,  or 
any  other  of  the  compounds  in  Class  i  are  present,  a  matte  will 
be  obtained  as  well  as  a  copper  button.  The  old  English  method 
(Cornish)  of  assaying  a  sulphide  ore  included  the  following  steps: 

i st.    Concentration  to  a  regulus  or  matte. 
2d.    Driving  off  most  of  the  sulphur  by  roasting. 
3d.    Reduction  of  black  copper  by  fusion. 
4th.  Refining  the  black  copper. 

This  necessitates  a  number  of  steps,  and  the  following  method 
will  be  found  to  simplify  the  process,  two  steps  being  used  in 
place  of  four: 

Class  I.  Sulphide  Ores. — These  ores  if  smelted  directly  would 
give  a  matte;  therefore  take  from  50  to  200  grammes  of  the  ore 
(through  30-  or  4O-mesh  sieve)  and  place  in  either  a  clay  or  iron 
roasting-dish.  If  the  latter  is  used,  it  must  be  well  coated  with 
ruddle  (Fe2O3+H2O)  or  chalk  before  using.  Place  this  in  a 
muffle  which  is  hardly  red  (have  the  coke  to  only  the  bottom  of 
the  mufHe)  and  heat  it  very  slowly,  to  avoid  caking  the  ore.  Stir 
the  ore  constantly  at  first  (see  notes  on  Gold  Assay,  page  132). 
The  object  of  this  work,  as  in  the  gold  work,  is  to  obtain  a  dead 
roast,  i.e.,  a  roast  in  which  neither  sulphates  nor  sulphides  are  left 
in  the  ore.  //  lime  is  present,  some  of  it  will  be  left  as  sulphate 
(2FeS  +  CaCO3  +  8O  =  Fe2O3  +  CaSO4  +  SO2  +  CO2) ;  everything 


ASSAY  OF  ORES  FOR   COPPER  AND   TIN.  215. 

else  will  be  in  the  state  of   oxides.     We   shall  probably  have 
CuO,  Fe2O3,  Fe3O4,  SiO2,  etc.,  in  the  ore  at  the  end  of  the  roast.. 
The  following  are  some  of  the  reactions  : 

Cu2S,FeS2+  30  =  2CuS  +  FeO  +  SO2  ; 


Cu2S  +  2CuSO,  -  2Cu2O  +  3SO2. 

Some  of  the  sulphates  and  arseniates  formed  during  the 
roast  may  be  reduced  by  the  addition  of  carbon,  and  the  sul- 
phides and  arsenides  so  formed  are  then  broken  up  with  the 
evolution  of  SO2  and  As2O3.  Some  sulphates,  like  those  of  iron 
and  copper,  may  also  be  broken  up  by  heat  alone,  forming  CuO 
and  SO3,  the  latter  breaking  up  into  SO2  and  O  : 

CuSO4=CuO  +  SO3; 
2FeS04  =  Fe203+S02+S03. 

Sulphate  of  lime  cannot  be  broken  up  by  either  method., 
The  final  temperature  should  be  almost  as  high  as  when  scorifying^ 

After  the  dead  roasted  ore  has  been  cooled  and  weighed, 
sift  it  through  a  sieve  to  remove  any  scales  or  lumps.  If  either 
of  these  is  present,  grind  through  the  same  sieve  the  ore  was- 
originally  put  through  (30  or  40  mesh)  and  mix  thoroughly  with. 
the  rest  of  the  ore. 

The  next  step  is  the  same  as  No.  3  in  the  English  method,  i.e.,. 
to  smelt  the  ore  with  suitable  fluxes  and  obtain  a  button  of  black 
copper.  If  a  matte  results  in  addition  to  the  black  copper,  the 
ore  contains  lime  or  it  is  not  sufficiently  roasted.  Roast  a  fresh 
portion  of  the  ore,  or  else  roast  the  matte  and  smelt  the  roasted 
product  as  if  it  was  an  ore. 

Fusion.  —  Applicable  also  to  ores  of  Class  II.  In  making  the 
fusion,  the  following  should  be  borne  in  mind. 

i  st.  The  slag  should  be  liquid,  and  as  nearly  neutral  as  pos- 
sible. 

2d.  The  amount  of  flux  should  be  as  small  as  possible,  and 
the  temperature  so  high  as  to  have  the  whole  assay  finished  in 
20  to  30  minutes  at  the  outside.  If  the  assay  is  kept  in  the  fire 
too  long,  iron  and  other  impurities  are  apt  to  be  reduced. 


0  ^ 

-    *-*• 


2 1 6  NOTES   ON  ASSAYING. 

3d.  All  reagents,  such  as  soda  and  argols,  should  be  free  from 
sulphur;  for  this  reason  use  cream  of  tartar,  in  place  of  argols,  as 
a  reducing  agent,  and  the  best  of  carbonate  of  soda. 

If  these  contained  sulphur,  there  would  be  a  copper  matte 
formed  during  the  fusion,  and  the  object  of  the  roasting  would 
be  rendered  useless. 

The  soda  and  borax  should  be  melted  in  an  iron  ladle  or  kettle 
before  using.  This  drives  off  the  water  present,  and  the  fusion 
for  copper  is  not  only  made  more  quickly  but  more  quietly. 

The  following  charges  may  be  tried.     (Use  E  or  F  crucibles.) 

ABC 

Ore,  grammes....   25       30       25. 

Cream  of  tartar,  . . .  .    10       20        2  charcoal 

Soda,  "        25       10      30 

Borax  glass,  "        ....     4       10       10  silica 

Use  no  cover  of  sail. 

Charge  A  is  for  an  ore  where  the  gangue  is  acid. 
Charge  B  is  more  of  a  neutral  charge,  and  C  is  for  an  ore 
where  the  gangue  tends  to  be  basic. 

These  charges  may  not  answer  for  every  ore,  but  having  made 
two  fusions,  one  of  A  and  one  of  B,  and  seen  the  resulting  slag 
and  button,  it  is  easy  to  make  changes  in  the  next  fusion.  That 
is,  if  the  slag  is  glassy  and  too  acid,  add  some  basic  flux  like  soda 
or  iron  oxide;  if  too  basic,  add  silica  or  borax  glass.  If  the  slag 
is  red,  due  to  Cu2O,  it  is  either  too  acid  or  insufficient  reducing 
agent  has  been  used. 

The  ore  and  fluxes  may  be  mixed  in  the  crucible,  and  the 
crucible  then  heated,  or  the  crucible  may  be  heated  red-hot  and 
the  charge  then  added.  The  latter  method  makes  the  shorter 
fusion,  but  the  charge  is  apt  to  dust  when  put  in  a  hot  crucible. 

Remove  the  crucible  from  the  fire,  allow  to  stand  and  break 
when  cold. 

Weigh  copper  button  and  calculate  the  percentage  in  the  raw  ore. 
Unless   an   ore   contains   lime,    duplicate   results   agree   very 
closely,  and  should  come  within  .2  per  cent  of  each  other  and 
.3  per  cent  of  the  wet  analysis. 

Abroad,  the  copper  buttons  obtained  in  a  fusion  are  often 
refined  by  putting  the  button  in  a  crucible  that  has  been  pre- 
viously used,  or  one  that  has  been  glazed  with  borax  glass,  cover- 


ASSAY   OF  ORES  FOR   COPPER  AND   TIN. 


ing  it  up  and  heating  it  red.  As  soon  as  the  copper  is  melted, 
remove  the  cover,  add  10  grammes  of  refining  flux,  replace  the 
cover,  and  in  a  few  minutes  remove  the  crucible  from  the  fire. 
Either  allow  fusion  to  cool  in  the  crucible,  or  else  pour. 

Refining  Flux. — i  part,  by  measure,  of  salt ;  2  parts,  by  meas- 
ure, of  cream  of  tartar;  3^  parts,  by  measure,  of  nitre.  Mix 
thoroughly. 

Class  II. — These  ores,  if  entirely  free  from  sulphides,  require 
no  roasting  and  are  fused  directly  by  some  one  of  the  charges 
given  under  Class  I. 

Class  III.  Ore  Carrying  Native  Copper. — Ores  belonging  to 
this  class,  for  instance  those  from  the  Lake  Superior  region 
may  be  treated  by  the  following  method,  which  has  the  great 
advantage  over  others  in  that  it  is  well  adapted  to  large  amounts 
of  rich  ore  or  concentrates  in  a  coarse  condition.  The  amount 
used  for  assay  is  rather  impracticable  for  chemical  work,  and  if 
a  small  amount  is  taken,  it  is  liable  to  be  an  incorrect  sample. 
If  this  small  amount  happens  to  represent  an  accurate  sample, 
the  ore  will  necessarily  have  to  be  pulverized  much  finer  to  obtain 
satisfactory  results,  and  the  metallic  particles  render  this  very 
difficult. 

The  fluxes  vary  according  to  the  gangue  or  the  foreign  matter 
in  the  mineral.  In  ' '  Modern  Copper  Smelting  "  Dr.  E.  D.  Peters 
.gives  the  following: 


No. 

Mineral 
Per 
Cent 
Cu. 

Weight 
in 
Grains. 

Borax 
Glass, 
Grains. 

Soda, 
Grains. 

Slag, 
Grains. 

Potas- 
sium Bi- 
tartrates, 
Grains. 

Sand, 
Grains. 

Iron  Ore, 
Grains. 

I 

2 

•2 

92 
86 
60 

IOOO 
IOOO 

=;oo 

60 
60 

IOO 

55 
60 
80 

2OO 

180 

300 
300 

2.OO 

4 

32 

soo 

ItjO 

1  60 

•JQO 

I  tCO 

1 

20 

•2C 

500 

ZOO 

190 
I4O 

200 
I4O 



300 

2OO 

170 

IOO 

t 

5  to  20 

500 

2OO 

200 

300 

*  Calumet  and  Hecla  tail-house  mineral.  f  Rich  slag  from  refining. 

"The  percentage  of  slag- forming  materials  being  so  small  in 
Nos.  i  and  2,  it  requires  but  a  slight  amount  of  borax  and  soda 
to  flux  them,  while  an  addition  of  neutral  slag  is  necessary  to 
protect  the  molten  copper.  A  smaller  quantity  of  the  ore  is 


2i8  NOTES  ON  ASSAYING. 

weighed  out  in  the  succeeding  assays,  as  they  are  so  poor  in  copper 
that  a  large  amount  of  flux  is  required  by  the  great  quantity  of 
gangue,  so  that  the  capacity  of  the  ordinary  crucible  would  be 
greatly  exceeded  if  1000  grains  were  used." 

"No.  3  mineral  contains  just  sufficient  ferric  oxide  to  form  a 
good  slag  with  the  mixture  given;  while  in  Nos.  4  and  5  this  sub- 
stance, as  well  as  metallic  iron,  increases  to  such  an  extent  as  to 
require  the  addition  of  a  considerable  proportion  of  sand  to  flux 
this  base  and  to  prevent  the  adulteration  of  the  button  with  metal- 
lic iron.     The  sample  of  Calumet  and  Hecla  tail-house  mineral 
given  is  typical  of  the  treatment  of  very  silicious  material.     There 
is  nothing   remarkable  in  the  considerable  proportion  of  borax 
(an  acid  flux)  used  with  even  highly  quartzose  ores ;   for,  in  addi- 
tion to  the  fluxing  powers  of  the  soda  that  it  contains,  a  borosili- 
cate  is  very  much  more  fusible  than  a  simple  silicate.     No  pecu- 
liarities exist  in  the  execution  of  this  assay;    the  ore  and  fluxes 
are  thoroughly  mixed  on  glazed  paper  and  covered  with  a  thin 
layer  of  potassium  bitartrate,  after  being  poured  into  the  crucible. 
"The  results  obtained  by  this  method  are  surprisingly  accurate. 
Duplicate  determinations  of  the  lower-grade  samples  seldom  vary 
more  than  o.i  or  0.2.     A  difference  of  0.4  per  cent  is  a  rare  occur- 
rence, even  in  the  higher  classes  of  mineral,  where  the  size  of  the 
metallic  fragments  renders  the  sampling  and  even  the  weighing 
out  of  a  correct  assay  a  matter  of  some  uncertainty." 

See  also  an  article  by  Mr.  G.  L.  Heath  in  the  Engineering  and 
Mining  Journal,  April  20,  1895,  "Copper  Assaying  as  Used  in  the 
Lake  Superior  Region." 

Copper  ores,  ingots,  cakes,  and  bars  are  generally  bought  on 
the  dry  assay,  and  the  dry  assay  is  considered  to  be  what  the  wet 
analysis  gives,  less  i .  3  per  cent.  That  is  to  say,  if  the  wet  analysis 
of  an  ore  gives  10  per  cent  copper,  it  is  settled  for  on  the  basis  of 
8.7  per  cent. 

The  difference  between  two  wet  analyses  should  not  exceed 
.2  of  i  per  cent. 

In  actual  smelting  operations  the  waste  slag  often  carries  less 
than  \  per  cent  copper,  but  it  is  safe  to  figure  on  a  loss  of  .75 
per  cent. 


ASSAY  OF  ORES  FOR  COPPER  AND   TIN.  219 


ASSAY  OF  ORES   FOR  TIN. 

Tin  melts  at  232°  C.  Atomic  weight  =119.  Sp.  gr.  =  7.25. 
Has  the  property  of  crackling  or  creaking  when  bent.  Tin  is 
found  in  few  localities  compared  with  the  other  metals  already 
taken  up,  and  is  seldom  discovered  in  the  metallic  state.  It 
occurs  both  in  veins  and  in  alluvial  deposits.  The  most  im- 
portant ore  is  cassiterite  (SnO2)  or  tinstone,  and  this  is  the  source 
from  which  most  of  the  tin  of  commerce  is  obtained.  The  chief 
deposits  are  those  of  the  Straits  Settlements,  Islands  of  Banka 
and  Billiton,  Bolivia,  Australia,  England,  and  Saxony.  More 
than  three-fourths  of  the  world's  production  comes  from  the 
first  three,  which  are  alluvial  deposits.  The  others  are  vein 
deposits.  Stannite  (sp.  gr.  4  3-4.52),  a  compound  of  Sn,  S,  Fe,, 
Cu,  and  sometimes  zinc,  is  also  found,  especially  in  South 
America,  though  it  is  not  as  common  as  cassiterite. 

The  color  of  the  oxide  may  be  black,  brown,  reddish  yellow, 
red,  and  brownish  white.  The  streak  is  white  to  brownish. 
When  pure  the  ore  contains  78.67%  of  Sn.  Sp.  gr.  =  6.8  to  7.1. 
The  impurities  most  frequently  associated  with  the  oxide  are 
pyrite,  arsenopyrite,  wolframite  (tungstate  of  Fe  and  Mn),  chal- 
copyrite,  titaniferous  iron,  columbite,  iron  oxide,  tourmaline,  and 
sometimes  blende  and  galena.  To  determine  whether  a  mineral 
is  SnO2,  fuse  some  of  the  fine  mineral  in  a  porcelain  crucible  or 
similar  vessel  with  3  or  4  times  the  amount  of  KCN  and  dissolve 
mass  in  water.  A  tin  globule  or  globules  will  be  found  if  the 
mineral  is  SnO2.  Or  fuse  a  mixture  of  the  mineral,  sodium  car- 
bonate, and  charcoal  on  charcoal  in  the  reducing  flame  of  a  lamp 
or  candle. 

When  in  veins  the  gangue  generally  consists  of  granite,  slate, 
syenite,  quartz,  or  feldspar,  and  often  carries  garnets  and  zircons^ 
Fluorspar  is  also  frequently  present,  and  by  some  is  considered 
a  good  indicator  of  tinstone. 


220  NOTES  ON  4SS4YING. 

Portions  of  the  deposits  are  often  very  rich,  but  the  average 
of  the  ore,  whether  from  veins  or  placers,  carries  only  i%  to  5% 
SnO2.  On  this  account,  samples  can  very  rarely  be  assayed  by 
iire  or  even  analyzed  in  the  wet  way  directly. 

Owing  to  its  high  specific  gravity,  however,  we  can  resort  to 
^washing  and  concentration,  thus  separating  it  from  the  gangue 
-and  some  of  the  other  impurities.  Wolframite,  unfortunately, 
has  a  specific  gravity  (7.2  to  7.5)  slightly  higher  than  tin  oxide, 
which  necessitates  a  special  purification  later  on,  when  this  min- 
eral is  present. 

The  following  table  from  Mitchell's  Assaying  will  show  why 
It  is  necessary  to  concentrate  or  free  the  ore  from  its  gangue  as 
much  as  possible. 

Ore  used  in  grammes 10         10  10  10         10 

:SiO2  present  in  grammes 2.5         6.6-        10  15         30 

Tin  obtained  by  fire  assay 52%     43%         28%         10%       o% 

Tin  oxide  has  a  great  affinity  for  silica,  for  it  has  the  property 
of  acting  both  as  an  acid  and  as  a  base,  and  in  this  case  acts  as  a 
"base.  If  the  tinstone  carries  much  iron  oxide,  this  has  to  be 
removed  with  acids,  otherwise  the  resulting  tin  will  not  collect 
in  a  button,  but  will  contain  iron  and  be  a  porous  and  magnetic 
mass. 

An  ore  carrying  4  per  cent  Sn  is  considered  a  fine  ore;  so  it 
can  be  readily  seen  that  one  must  first  resort  to  concentration 
before  making  a  fire  assay.  This  is  also  the  better  plan  even 
before  attempting  a  wet  analysis,  unless  the  sample  submitted 
for  analysis  is  very  rich.  The  steps  in  the  assay  are  as  follows : 

i st.  Concentration. 

2d.    Roasting  the  concentrates. 

3d.    Panning  the  concentrates  and  boiling  in  aqua  regia. 

4th.  Panning  the  concentrates  again. 

5th.  Assaying  the  final  concentrates. 

If  the  concentrates  obtained  from  the  first  panning  are  very 
pure,  some  of  the  later  steps  may  be  omitted. 

Concentration. — Take  500  to  TOGO  grammes  of  ore,  crushed 
through  at  least  a  4o-mesh  sieve.  If  it  is  crushed  too  fine,  the 
SnO2  will  slime  badly;  still  it  must  be  fine  enough  to  liberate 


ASSAY  OF  ORES  FOR   COPPER  AND    TIN.  221 

the  SnO2  from  the  gangue.  Carefully  pan  or  van  the  ore  again 
and  again  until  no  more  concentrates  can  be  obtained.  Do  not 
pan  down  too  close,  for  if  a  little  gangue  is  left  with  the  con- 
centrates it  does  not  matter.  The  waste  matter  or  tailings  are 
thrown  away. 

Roasting. — The  concentrates  consisting  of  SnO2,  pyrite,  and 
whatever  heavy  material  there  happened  to  be  in  the  ore,  together 
with  a  small  amount  of  gangue,  are  dried  and  then  placed  in  a 
clay  or  an  iron  roasting-dish.  This  is  next  placed  in  a  muffle,, 
the  bottom  of  which  is  hardly  red,  and  slowly  heated.  When 
the  odor  of  SO2  can  no  longer  be  detected,  the  dish  is  taken  out, 
cooled,  and  a  little  fine  charcoal  stirred  into  the  ore.  This  reduces 
the  sulphates,  arseniates,  and  antimoniates  to  lower  forms  and 
enables  the  S,  Sb,  and  As  to  be  set  free,  and  is  especially  necessary 
when  arsenic  is  present.  Roast  again  and  repeat  until  a  dead 
roast  is  obtained.  Everything  in  the  concentrates  should  now' 
be  in  the  state  of  oxides.  They  can  now  be  panned  to  remove 
the  oxides  of  iron  and  silica  and  then  treated  with  acid,  or  they 
can  be  treated  with  acid  directly  and  then  panned. 

Treatment  with  Acid. — SnO2  is  insoluble  in  aqua  regia^ 
therefore  by  boiling  the  concentrates  in  this  we  practically  get 
rid  of  everything  except  some  SiO2,  TiO2,  and  compounds  insoluble 
in  aqua  regia.  If  much  SiO2  is  present,  pan  again.  In  some 
cases  it  is  well  to  grind  the  tailings  fine  from  this  concentration 
and  pan  again.  Dry  the  total  concentrates,  weigh  and  grind 
through  an  8o-mesh  sieve. 

Assaying. — The    concentrates    are    now  ready  for    assayingr 
and  this  may  be  done  by  various  methods.    Among  the  most 
approved  are  the  following: 

First  Method. — (Level's  Cyanide  of  Potash.) — This  method  has 
always  given  me  the  most  satisfactory  results,  so  it  is  placed  first. 
On  clean  ores  or  concentrates  it  is  very  accurate,  but  when  the  ore 
or  the  concentrates  contain  much  foreign  matter  the  assay  is 
rendered  much  more  difficult  and  the  time  of  fusion  has  to  be, 
increased. 

Take  5  or  10  grammes  of  concentrates  and  mix  with  four 
times  as  much  KCy,  C.P.  (KCy  is  a  deadly  poison  /) 


222  NOTES  ON  ASSAYING. 

Have  a  good  layer  of  KCy  in  the  bottom  of  the  crucible, 
next  put  in  the  mixture  of  concentrates  and  KCy,  and  then  place 
a  layer  of  KCy  on  top  of  all. 

Crucible  is  a  Battersea  A  or  similar  close-grained  crucible. 


Layer  of  KCy  (through  8). 
Concentrates  and  KCy  mixed. 
Layer  of  KCy  (through  8). 

Heat  very  slowly  at  first  and  just  fuse  to  reduce  the  SnO2  to 
"Sn  and  then  keep  just  fused  for  20  to  30  minutes.  Increase  tem- 
perature 10  to  15  minutes  longer  and  then  take  from  the  fire, 
tap  gently,  and  transfer  to  some  place  where  the  fumes  will  not  be 
tarried  into  the  laboratory.  The  purer  the  SnO2  is  the  shorter 
the  period  of  fusion;  with  some  ores  the  fusion  has  been  com- 
pleted in  10  minutes  with  good  results,  but  as  a  general  thing 
the  ordinary  concentrates  will  require  the  above  time  to  make  the 
fusion  satisfactory.  Certainly  the  more  impure  the  concentrates 
are  the  longer  the  fusion  must  be.  Never  have  the  fusion  boil, 
jor  low  results  will  be  obtained. 

Allow  the  crucible  to  become  perfectly  cold.  (Tin  melts  at 
232°  C.)  Break  the  crucible  and  place  it  and  contents  in  a  dish 
and  cover  with  water.  If  the  decomposition  of  the  ore  is  com- 
plete, we  shall  have  a  nice  bright  tin  button,  with  perhaps  a  few 
prills  or  small  buttons.  If  the  fusion  is  incomplete,  we  shall  find 
some  ore  still  undecomposed.  The  great  advantage  of  this 
method  of  assay  is  that  although  one  works  with  an  expensive 
and  poisonous  reagent,  one  can  see  at  the  end  of  the  fusion 
what  has  actually  been  done. 

The  KCy  should  be  C.P.  The  impurities  are  generally 
chloride,  carbonate,  and  cyanate  of  potassium  or  of  sodium. 

Some  assayers  recommend  a  cover  of  salt,  but  I  consider 
a  layer  of  KCy  amply  sufficient. 

Ten  grammes  of  concentrates  have  always  given  me  higher 
results  than  5.  Report  any  and  all  results  in  percentage  on  the 
joriginal  ore  used.  Results  on  concentrates  and  original  ore 


ASSAY  OF  ORES  FOR   COPPER  AND   TIN.  223 

should  agree  very  closely  and  ores  carrying  one-half  per  cent  Sn 
can  be  assayed  satisfactorily  by  the  foregoing  method  of  concen- 
tration. 

Second  Method  (German  Assay). 

Rich  ore  or  concentrates  (through  80)     5         5  10  )  ,  . 

.  ,  ,         ,   Q  ,  >  Mix  in  bottom  of  crucible 

Charcoal  (through  So) i         i  2  } 

Flour 5        3  5  ^ 

Bicarb,  soda 10         5  —  >  Mix  and  put  on  top 

Bicarb,  potash 10         5  20 ) 

Borax  glass —       £  inch      2  grammes 

Cover  of  salt  in  each  case,  and  a  small  piece  of  charcoal  on  top. 

Heat  very  slowly  at  first,  say  about  20  minutes,  and  then  fuse 
until  charge  is  quiet  and  foaming  ceases,  about  i  to  ij  hours.. 
The  results  are  good,  but  the  button,  owing  to  the  high  heat,  is 
apt  to  contain  a  small  amount  of  iron.  If  a  small  chip  cut  off 
the  button  is  not  magnetic,  the  amount  of  iron  is  very  small. 

Third  Method. — This  method  is  given  by  Mitchell,  who  uses 
larger  amounts  of  material  than  I  give,  but  in  the  same  ratio. 
Personally  I  have  never  had  any  success  with  it. 

Reactions. 

Ore  or  concentrates 12  grammes  "j       ju      Na2Co3+heat  =  Na2O-f-Co2; 

Argols 3        "          1  .g|     Na20+C        =2Na+CO; 

Sodium  carbonate 9         "          I    ^  §     4Na+  SnO2    =  2Na2O+  Sn. 

Lime ii       "         J        £ 

"Mix  well  together,  place  in  a  crucible  which  the  mixture  half 
fills,  cover  with  a  small  quantity  of  sodium  carbonate  and  5 
grammes  of  borax.  Place  the  whole  in  the  furnace  with  the 
necessary  precautions,  raise  the  heat  very  gently,  and  keep  it  at 
or  below  a  dull  red  heat  for  at  least  20  minutes,  then  gradually 
increase  until  the  whole  flows  freely.  Remove  the  crucible,  tap 
it  as  for  copper  assay,  and  allow  to  cool.  When  cold,  break  it, 
and  a  button  of  pure  metallic  tin  will  be  found  at  the  bottom,  and 
a  flux  perfectly  free  from  globules  and  containing  no  tin." 

Fourth  Method. — Take  25  to  50  grammes  of  fine  concentrates, 
place  them  in  a  graphite  or  charcoal-lined  crucible,  and  cement 
the  cover  on  firmly,  leaving  a  small  opening.  Heat  at  a  dull  red 
for  15  minutes  and  then  at  a  bright  red  for  10  minutes.  Remove 
the  crucible  with  care  and  do  not  tap.  The  results  are  generally 
low,  owing  to  prills  and  small  buttons. 


CHAPTER  VEIL 
PLATINUM  AND  THE  PLATINUM  GROUP. 

THE  platinum  group  of  metals  consists  of  platinum,  indium, 
osmium,  palladium,  ruthenium,  and  rhodium. 

Iridosmium  is  an  alloy  of  iridium  and  osmium.  If  we  divide 
the  group  by  atomic  weights,  it  is  seen  that  platinum,  iridium,  and 
osmium  are  very  closely  associated;  likewise  palladium,  ruthe- 
nium, and  rhodium. 

The  group  may  perhaps  be  further  divided  into  platinum  and 
palladium,  rhodium  and  iridium,  osmium  and  ruthenium.  In 
regard  to  the  metals'  affinity  for  oxygen,  we  find  that  the  oxides 
of  osmium  and  ruthenium  are  volatile,  or  partly  so ;  that  iridium, 
palladium,  and  rhodium  oxidize  when  heated  with  free  access  of 
air,  but  the  oxides  break  up  upon  further  and  higher  heating  into 
the  metal  and  oxygen. 

Platinum  does  not  oxidize,  although  it  can  be  thrown  down 
from  solution  as  an  oxide.  Russia  and  the  United  States  of 
Colombia  are  the  chief  sources  of  supply,  but  the  metal  is  much 
more  widely  distributed  than  is  generally  known.  Although 
occurring  most  commonly  in  grains  and  nuggets  in  alluvial  sands 
and  placers,  it  has  been  found  in  rock  in  place.  Fine  grains 
have  been  found  in  quartz,  but  the  basic  rocks,  like  olivine,  ser- 
pentine, peridotite,  and  chromite,  are  the  ones  from  which  most 
platinum  has  been  derived,  for  pieces  of  these  rocks  are  often 
found  attached  to  nuggets. 

Platinum  grains  are  grayish  white  in  color,  and  their  specific 

gravity  depends  upon  the  other  metals  or  those  of  the  platinum 

224 


PLATINUM  AND   THE  PLATINUM  GROUP.  22$ 

group  associated  or  alloyed  with  them.  The  grains  or  nuggets, 
are  seldom  pure,  and  not  only  contain  the  members  of  the  group,, 
but  analyses  have  shown  gold,  manganese,  iron,  and  copper. 
The  last  two  are  very  common  impurities  and  some  nuggets  have: 
carried  as  high  as  17%  iron.  It  is  also  interesting  to  note  that: 
considerable  platinum  has  been  found,  in  several  instances,  in 
copper  sulphides  and  tetrahedrite. 

Platinum  does  not  amalgamate  even  when  both  it  and  the 
mercury  are  heated.  When  immersed  in  sodium  amalgam,  the 
mercury  seems  to  adhere  to  its  surface,  but  it  does  not  really 
amalgamate.  This  property  can  often  be  taken  advantage  of  to 
remove  the  platinum  grains  in  an  ore  after  the  removal  of  the 
gold  by  mercury  alone. 

The  sp.  gr.  of  the  grains  has  been  found  to  be  anywhere 
from  13  to  19  and  the  purity  from  50  to  86%  Pt.  The  sp.  gr. 
of  melted  platinum  is  between  19  and  20,  while  that  of  the  metal 
when  hammered  is  between  20  and  21.5. 

Sperrylite,  an  arsenide  of  platinum  (PtAs2),  sp.  gr.  10.6,  is 
the  only  platinum  mineral  at  present  known,  and  was  discovered 
in  1888  by  F.  L.  Sperry  in  the  Sudbury  district,  Ontario,  Canada. 
Since  then  it  has  been  found  in  several  places  in  the  United  States.. 
The  only  other  known  mineral  of  the  group  is  laurite,  a  sul- 
phide of  ruthenium  and  osmium. 

The  table  on  pages  226  end  227  gives  some  of  the  properties; 
of  the  group,  to  which  have  been  added  silver  and  gold. 

Qualitative  Tests. — If  the  ore  is  very  low  grade,  it  had  bet- 
ter be  concentrated  and  the  concentrates  taken  for  the  test- 
If  free  gold  is  present,  remove  it  with  mercury. 

Treat  the  ore  or  concentrates  with  aqua  regia,  evaporate 
several  times  to  a  syrup  with  HC1,  in  order  to  remove  all  the 
HNO3.  Finally,  take  up  in  water  and  a  few  drops  of  HC1,  boil 
and  filter.  The  Pt  should  be  in  solution  as  bichloride  (PtCl4). 
This  solution  can  now  be  tested  for  Pt  in  either  of  two- 
ways: 

i.  Take  a  small  amount  of  the  cold  solution  and  add  to  it 
a  strong  solution  of  potassium  iodide.  If  Pt  is  present  the  solu- 
tion will  become  a  deep  red  color  (platinum  iodide).  The  test 


226 


NOTES   ON  ASSAYING. 

TABLE  OF  SOLUBILITY  OF  SILVER, 


Silver. 

Gold. 

Platinum. 

Iridium. 

Atomic  wght 

107.9 

197.2 

194.9 

193 

Specific  gr. 

10.4-10.7  \ 

I5~I9-3  native 
19  .  3  pure 

Melted  19-20 
Hamm'd  20—21.5 

j-            22.42 

Fusibility 

964° 

1064°  C. 

1  760°  to  1765° 

About  1950° 

Hardness 

Below  7 

Color  of 

Brilliant 

Yellow 

Grayish  white 

Steel-white 

metal 

white 

Powder 

Black 

Steel-gray 

Heat  (air) 

Not  oxidized 

Not  oxidized 

Not  oxidized 

Oxidizes    when 

heated    in    air, 

but  oxides  break 

up,  when  f  u  r  - 

ther  heated,  into 

metal  and  oxy- 

gen 

HsSO, 

Soluble 

Insoluble 

Insoluble 

Insoluble     when 

alloyed       with 

silver,    if     due 

precautions   are 

taken 

H2S04 

Partly   soluble. 

Partly        soluble 

(fuming) 

Ir   lessens   the 

when     alloyed 

solubility 

with  Ag 

HNO, 

Soluble 

Insoluble 

Soluble  when  al- 

Insoluble. Partly 

loyed      with 

soluble      when 

Ag  12,  Pt  i;  or 

alloyed       with 

AgI2,Pt  I,AU2 

silver 

Aqua  regia 

AgCl  precipi- 

Soluble 

Soluble.    Dilute; 

Soluble  when  al- 

tates 

i   to  3   is  the 

loyed  with  Pt. 

best.      Said  to 

Soluble     in 

be       insoluble 

strong  aqua  re- 

when    alloyed 

gia.    Insoluble 

with       certain 

in  dilute.  Com- 

percentages of 

pact  iridium  is 

iridium  or  with 

said    to   be    in- 

rhodium 

soluble     in    all 

acids 

Sodium     hy- 

pochlorite 
Fused      with 

Oxidizes  but  does 

potassium 

not  dissolve  it 

disulphate 

PLATINUM  AND   THE   PLATINUM  GROUP. 


227 


GOLD,  AND  THE  RARE  METALS. 


Osmium. 

Palladium. 

Ruthenium. 

Rhodium. 

Iridosmium 
or 
Osmiridium. 

191 

106.5 

101.7 

103 

22.48 

11.4 

11-12 

12.  I 

18-21.5 

Melted  only  in 

About   wrought 

Over    2500°    C. 

Higher  than  Pt 

the  electric  arc 

iron 

Higher     than 

rhodium 

Above  7 

4-5-5 

Below  7 

6-7 

Bluish 

Steel-gray     or 

Grayish  white 

Whitish  gray 

Tin-white  to 

white.  Darker 

steel-gray 

Bluish 

[than  Pt 

Purple-black 

Black 

Oxidizes.    OsO4 

Oxidizes  on  heat- 

Oxidizes.   RuO 

Oxidizes    when 

very  volatile 

ing,    but    ox- 

and RuO2  vol. 

heated,      but 

ides  break  up 

atile.      Ru2O3 

oxides    break 

into  metal  and 

(bluish  black) 

up  into  metal 

oxygen.  Metal 

not     volatile; 

and  oxygen 

resumes      its 

decompo  s  e  d 

color 

by  heat 

Insoluble.      In- 

Slightly soluble, 

Insoluble  when 

Insoluble.  There 

Insoluble 

tensely  ignited 

especially 

alloyed    with 

are  two  modi- 

Os is  insolu- 

when alloyed 

silver   if    due 

fications      0  f 

ble  in  all  acids. 

with  Ag 

precautions 

Rh.  Compact 

Silver  does  not 

are  taken 

and     precipi- 

affect solubil- 

tated 

ity 

Soluble  with  dif- 

ficulty.   Solu- 

ble when  al- 

loyed with  Au 

and  Ag 

Soluble  with  for- 

Partly soluble 

Insoluble 

Compact;  insol- 

Insoluble 

mation        o  f 

when  alloyed 

uble.      Ppt'd, 

Os04 

with     A  g  . 

slightly   solu- 

HNO3+HNO2 

ble 

with  ease 

Insoluble 

Soluble.     PdCL 

Slightly  soluble. 

Is  said  to  be  sol- 

Insoluble 

and     PdCl4 

Oxides  insol- 

uble when  al- 

separate   out 

uble 

loyed       with 

upon  long 

other  rare 

standing 

metals     and 

Cu,  but  not  to 

be   when    al- 

loyed with  sil- 

ver or  gold 

Soluble    when 

finely  divided 

Soluble 

Attacked 

Soluble 

228  NOTES  ON  ASSAYING. 

is  very  delicate,  ?.nd  if  much  Pt  is  present,  only  a  very  small' 
amount  of  the  solution  to  be  tested  should  be  taken.  Heat  will, 
cause  the  color  to  disappear. 

2.  To  the  very  concentrated  solution  add  a  strong  solution 
of  NH4C1  or  the  salt  itself,  and  then  a  good  deal  of  alcohol.  Allow 
to  stand  for  24  hours  at  about  80°  C.,  when,  if  PL  is  present,  a  yellow 
precipitate  of  (NH3)2PtCl6  wil.  be  thrown  down.  Any  gold  pres- 
ent as  AuCls  will  lemain  in  solution.  If  the  ore  sperrylite,  the 
arsenide  of  platinum,  is  to  be  tested  for,  take  a  small  portion 
and  drop  it  on  a  hot  piece  of  platinum-foil:  As2O3  will  be  given 
off,  leaving  spongy  excrescences  of  platinum  similar  to  the  foil. 

S  perry,  ite  is  only  partly  soluble  in  aqua  regia,  and  is  not 
attackel  by  hydrofluoric  acid. 

Quantitative  Analysis.*— Quantitative  work  upon  platinum 
ores,  especially  where  other  rare  metals  are  present,  is  very  diffi- 
cult, and  most  of  the  methods  are  long  and  complicated. 

ASSAY    OF   THE   SAND3    AND  ORES. 

I  prefer  to  divide  platinum  ores  into  three  classes: 

1.  Ores  carrying  no  metallic  grains,  which  can  be  assayed 
directly. 

2.  Ores  with  value  in  concentrates  but  carrying  no  metallic 
grains,  which  are  too  poor  to  assay  without  a  previous  concentration. 

3.  Ores  carrying  metallic  grains. 

CLASS  I.  Crush  these  ores  through  a  i2o-mesh  sieve,  assay- 
them  exactly  as  if  assaying  ores  for  gold,  and  obtain  a  lead  button 
weighing  from  25  to  30  grammes.  If  ore  is  very  poor  take  5  A.T. 
or  more  and  assay  as  in  the  case  of  low-grade  gold  ores,  p.  130. 

CLASS  II.  Take  300  or  more  grammes  of  ore  (through  a  30-  or 
a  4o-mesh  sieve),  concentrate  it,  and  then  assay  the  concentrates. 

*  Bibliography  of  the  Pt  Group,  Dr.  J.  Lewis  Howe,  and  among  others  the  fol- 
lowing: St.  Claire,  Deville,  and  Debray,  Annals,  de  Chim.  et  de  Phys.  (3),  vol.  56- 
(1859),  p.  385;  Dr.  H.  Pirungruber,  Eng.  and  Min.  Journ.,  vol.  44,  p.  256;  E. 
Wiatt,  Eng.  and  Min.  Journ.,  vol.  44,  p.  273;  T.  Wilm,  Journ.  Chem.  Soc.,  vol. 
50  (1886),  p.  181;  also  Journ.  Soc.  Chem.  Ind.,  vol.  4  (1885),  p.  759;  Mitchell's 
"Assaying,"  p.  781;  Crookes'  "Select  Methods,"  pp.  446  to  476;  E.  Leidie, 
Bulletin  Societe  Chimique  (3),  vol.  25,  p.  9;  E.  Leidie  and  Quennessen,  Bulletin. 
Societe  Chimique  (3),  vol.  27,  p.  179. 


PL  A 'TIN 'UM  AND   THE  PLATINUM  GROUP.  229 

as  in  the  assay  of  concentrates  carrying  gold.  The  tailings  are 
thrown  away.  The  lead  button  from  this  fusion  should  weigh 
25  to  30  grammes  and  its  treatment  is  described  later  on.  Figure 
the  results  on  the  original  ore  taken. 

CLASS  III.  Ores  of  this  class  are  the  ones  most  frequently 
met  with,  and  their  preliminary  treatment  must  be  carefully 
conducted.  The  aim  is  to  remove  the  platinum  grains  as  far 
as  possible  and  to  make  all  the  grains  in  the  sample  into  rich 
lead  bullion. 

Samples  weighing  less  than  1000' grammes  should  be  crushed 
through  a  30-  or  4o-mesh  sieve.  Save  any  pellets  on  sieve.  Amal- 
gamate all  the  ore  to  remove  the  gold,  and  concentrate  to  a  small 
•amount  of  heads.  Remove  any  Pt  grains.  The  heads  and  tails 

Ore,  900  grammes 
Crushed  through  3o-mesh  sieve 

Au  +  Pt  grains  Ore 

Amalgamate  Amalgamate 


Ptg 

rains                         Au  amalgam 

Au  amalgam                         O: 

Dissolve  in  HNO3 

Au  weigh 
Conce 

Hg2(N03), 

itrate 

Pt  grains                             Conce  i 
/Crt 

itrates,  weigh                                       T 

sh  through  8o-mesh,  weigh 

Ore  (T}  assav 

Weigh 

I 
Melt  with  40  grammes 

or  more  of  lead  and  chill  quickly. 

I 
Weigh  bullion;  take  drillings 

and  cupel  several  portions. 

Figure  the  total  Pt  in  the  ore  (T)  and  the  lead  bullion,  and  base  the  final  result 
•on  the  9oo-gramme  sample. 


230  NOTES  ON  ASSAYING. 

should  all  be  ground  through  an  8o-mesh  sieve  and  pellets  saved. 
Assay,  as  usual,  the  material  through  an  8o-mesh  sieve. 

The  pellets  are  all  put  together  and  melted  with  lead.  This 
bullion  should  be  chilled  instantly,  to  prevent  segregation  of  the 
metals,*  drilled  or  cut  up  into  pieces,  and  assayed  as  described 
later  on. 

A  tree  of  the  treatment  is  given  on  the  preceding  page. 

This  method  eliminates  the  question  of  small  samples  disa- 
greeing, owing  to  uneven  distribution  of  pellets. 

Large  samples  should  be  treated  as  follows :  Crush  3  to  5  kilos 
through  a  3o-mesh  sieve.  Save  any  pellets.  Amalgamate  all  the 
ore  to  remove  gold.  Pan  out  the  amalgam  and  remove  the  con- 
centrates. Recover  all  the  platinum  grains  possible  from  the 
concentrates.  The  heads  and  tails  are  dried,  thoroughly  mixed, 
and  a  sample  of  at  least  700  grammes  taken.  The  Pt  grains 
so  far  obtained  are  weighed,  melted  together  with  lead,  and  results 
based  on  3  to  5  kilos.  The  700  grammes  are  treated  as  previously 
described,  and  all  grains  are  kept  separate,  wrapped  in  lead,  and 
cupelled. 

This  button  need  not  be  analyzed,  because  the  analysis  of 
the  main  lot  of  pellets  for  the  other  rare  metals  will  be  sufficiently 
accurate  for  this  or  any  other  residue. 

The  work  so  far  has  given  us,  from  Classes  I  and  II,  lead 
buttons  carrying  silver  and  gold,  if  present  in  the  sample,  together 
with  platinum  and  any  of  the  rare  metals,  or,  from  Class  III, 
rich  lead  bullion  carrying  Pt  and  the  rare  metals.  The  advan- 
tage of  a  large  button  rich  in  Pt  over  a  small  low-grade  lead 
button  is  that  drillings  can  be  taken  from  the  former  and  sev- 
eral assays  made  instead  of  relying  upon  one.  We  can  now 
proceed  as  follows: 

Cupel  the  lead  button  (Classes  I  and  II)  or  the  drillings  from 
the  bullion  as  usual,  except  towards  the  end,  when,  if  much  Pt  is 
present,  the  heat  must  be  very  high  in  order  to  remove  the  last 
traces  of  lead.  The  presence  of  a  small  amount  of  Pt  makes  the 

*Ed.  Mathey,  Chem.  News,  vol.  61,  p.  HI,  "Liquation  of  Au  and  Pt 
Alloys." 


of 


PLATINUM  AND    THE  PLATINUM  GROUP.  231 

final  bead  crystalline  on  the  surface  and  often  covered  with 
irregularities.  If  very  much  Pt  is  present,  the  button  will  stick 
to  the  cupel,  be  spread  out,  irregular,  and  have  a  gray  mossy 
appearance.  Such  buttons  are  liable  to  contain  lead,  for  it  is 
extremely  difficult  in  such  cases  to  remove  the  last  traces  of 
this  metal. 

Care  should  be  exercised  in  hammering  the  beads  contain- 
ing any  of  the  platinum  group,  for  a  small  amount  of  lead  seems 
to  render  them  brittle  at  times. 

A.  Bauer  found  that  an  alloy  of  3  parts  Pb  and  i  part  Pt 
was  as  brittle  as  glass. 

From  now  on  the  difficulties  that  we  encounter  are  increased 
by  the  influence  which  silver  and  gold,  if  present,  have  upon  the 
solubility  0}  Pt  and  the  rare  metals,  as  well  as  the  influence  the 
rare  metals  have  upon  the  solubility  o]  each  other. 

The  best  method  of  procedure  seems  to  be  as  follows,  and  I 
am  indebted  to  the  following  students,  who  have  taken  theses 
on  the  analysis  of  Pt  ores  and  the  rare  metals,  for  much  of  the 
data:  H.  B.  Litchman  and  D.  C.  Picard,  class  of  1903,  and  R. 
B.  Williams  and  J.  R.  Marston,  class  of  1904. 

Determination  of  Ag,  Au,  Pt,  Ir,  and  Iridosmium. — Clean  the 
bead,  hammer  if  possible  (some  buttons  containing  Pt,  silver 
and  the  rare  metals,  or  a  certain  ratio  of  Pt  and  Ag  are  brittle) 
and  weigh  (a).  Part  in  strong  H2SO4,  boiling  three  times;  the 
silver  will  dissolve,  leaving  the  other  metals,  if  three  or  more 
parts  of  silver  are  present.  Much  care  must  be  used  in  this 
parting,  for  when  H2SO4  is  used  the  Au  and  Pt  are  liable  to  be 
left  in  a  finely  divided  condition.  Furthermore,  if  iridium  is  present 
and  it  is  finely  divided,  it  will  float  on  the  top  of  the  solution. 
In  such  cases  the  H2SO4  and  Ag2SO4,  after  cooling  somewhat, 
should  be  decanted  into  a  casserole  containing  H2O.  Cautiously 
pour  hot  H2O  into  the  parting-flask,  allow  to  stand  some  time, 
and  again  decant,  repeat  twice  more,  when  the  Ag2SO4  should 
be  removed.  Filter  the  contents  of  the  casserole  through  a 
washed  filter.  Fill  the  parting-flask  with  hot  water  and  trans- 
fer contents  to  an  annealing  cup  or  porcelain  crucible,  allow- 


-232  NOTES  ON  ASSAYING 

ing  flask  to  stand  inverted  in  cup  at  least  five  minutes,  and  occa- 
sionally tapping  its  sides.  Wash  the  contents  of  the  filter  and 
transfer  it  and  its  contents  to  the  annealing  cup  with  the  rest  of 
the  metals.  Ignite  the  filter-paper  cautiously  and  finally  heat 
in  the  muffle.  Cool  and  weigh.  Sometimes  the  residue  sticks 
slightly  to  the  cup,  but,  as  a  rule,  not  badly.  This  residue  is 
~b,  and  the  difference  between  a  and  b  is  the  silver  in  the  ore. 

If  the  amount  of  silver  is  extremely  small,  this  result  can 
: serve  as  an  approximate  determination,  for  considerable  Ag  is 
lost  at  the  high  temperature  required  in  cupelling.  After  the 
Pt  and  other  elements  are  determined,  weigh  out  a  known  quantity 
of  Ag,  add  it  to  the  lead  button  from  another  assay  of  the  ore, 
run  a  check  at  the  same  time,  as  in  bullion,  cupel,  dissolve  but- 
tons in  HN  O3,  and  titrate  with  a  solution  of  salt.  Make  allow- 
ance for  the  silver  added  and  figure  the  results  as  in  the  assay 
of  silver  bullion. 

Add  to  the  residue  b  12  to  15  times  as  much  silver  alone 
-or  12  to  15  times  as  much  silver  and  i  or  2  times  as  much 
gold.  If  gold  other  than  free  gold  is  present  in  the  sample, 
do  not  add  gold;  wrap  in  6  to  8  grammes  of  lead  and  cupel. 
Clean  the  button,  roll  out,  and  drop  into  some  warm  HNO3 
(1.20  or  1.28  sp.  gr.).  All  of  the  silver  and  part  of  the  Pt  (75% 
to  95%,  if  gold  is  present)  will  go  into  solution.  If  gold  is  used, 
repeat  this  process  twice  more,  but  of  course  add  no  more  gold. 
"If  silver  alone  is  used,  repeat  until  all  the  Pt  is  dissolved.  The 
final  residue  should  consist  of  gold,  iridium,  and  iridosmium. 
Weigh  (c).  (c)  minus  any  gold  added,,  subtracted  from  (&),  is 
the  Pt  in  the  sample. 

The  residue  c  is  treated  for  a  few  minutes  with  dilute  aqua  regia, 

/ \  parts  HC1  \ 
i  part  aqua  regia  \f  F       HNQ  J  and  5  parts  H2O, 

which  dissolves  the  gold  and  any  Pt  that  might  be  present. 
Wash,  ignite,  and  weigh  residue  d.  Residue  c,  minus  any  gold 
•added,  less  d  is  the  gold  in  the  sample.  Treat  residue  d  with 


PLATINUM  AND   THE  PLATINUM  GROUP. 


233 


strong  aqua  regia,  which  dissolves  the  iridium,  leaving  the  iridos- 
mium  and  rhodium,  also  osmium  and  ruthenium,  if  these  last 
Lave  not  been  volatilized  during  cupellation. 


EXAMPLES. 


Residue  after  parting  in 

Residue  after 

Pt  and  Au 

After    strong 

Ir 

H2S04 

dilute  aqua  regia 

grammes 

aqua  regia 

grammes 

i.            .00388  grammes 

•00337 

.  0005  i 

.00327 

.00010 

Au,    Pt,    Ir,    Rh,    and 

Ir,  Rh,  Iridos- 

Rh and  Iri- 

Iridosmium 

mium 

dosmium 

2.            .00230  grammes 

.  00040 

.00190 

.00035 

.00005 

If  gold  is  absent  from  the  ore  and  Pt  alone  is  to  be  deter- 
mined, the  procedure  is  as  follows:  Cupel  the  lead  button  as 
described,  adding  2\  to  3  times  as  much  silver  as  the  amount 
of  Pt  supposed  to  be  present  in  the  sample.  Part  the  resulting 
bead  in  strong  H2SO4  and  weigh  the  residue  (x),  which  will  prob- 
ably be  grayish  black.  Treat  with  dilute  aqua  regia,  i.e.,  i  to 
5,  in  the  proportions  just  given,  or  else  i  to  3;  the  Pt  will 
go  into  solution,  and  if  any  residue  is  left  it  is  probably  Ir, 
Rh,  Ru,  or  iridosmium.  Dry,  ignite,  and  weigh.  The  dif- 
ference between  this  and  the  first  weigh  (x)  is  the  Pt  in  the 
sample. 

Care  in  Compelling. — Where  a  large  number  of  samples  con- 
taining gold  and  platinum  are  to  be  assaved  for  Pt  it  is  well  to 
classify  them  if  possible,  according  to  Pt  contents,  into  rich, 
medium,  and  poor  ores.  This  will  enable  one  at  the  time  of 
cupellation  to  place  those  rich  in  Pt  in  the  back  of  the  muffle, 
where  a  high  heat  is  necessary,  and  those  poor  in  Pt  in  front, 
where  litharge  crystals  can  be  obtained  as  usual.  If  this  is 
not  done  and  the  rich  and  poor  buttons  are  scattered  about  indis- 
criminately, the  high  heat  necessary  for  the  rich  ones  will  cause 
such  a  loss  of  gold  in  the  poor  ones  that  the  Pt  results  will  be 
far  too  high. 

Where  the  gold  is  to  be  determined,  and  in  all  espe- 
cially nice  work,  checks  should  be  run  as  in  the  assay  of 
bullion. 


234  NOTES  ON  ASSAYING. 

The  following  work,  done  by  Mr.  H.  B.  Litchman,  class  of  1903, 
is  of  interest  in  this  connection.  Pure  lead,  silver,  gold,  and  plati- 
num were  used  in  the  tests. 

Nos.  15,  16,  and  17  were  cupelled  in  the  middle  of  a  muffle 
heated  by  gas  and  then  pushed  back;  the  others  were  cupelled  in 
the  front  and  gradually  pushed  back  until  they  stood  at  the  back 
of  the  muffle.  All  of  them  were  left  in  the  furnace  i  minute 
after  blicking  at  a  very  high  temperature. 

Nos.  15, 19,  and  22  were  treated  with  10  c.c.  HNO3  (1.28  sp.gr.)> 
boiled,  10  c.c.  more  added  and  the  boiling  continued.  No.  22 
was  treated  with  a  third  portion.  No.  15  did  not  break  up;  19 
and  22  broke  up,  rendering  the  solution  brown  and  turbid,  due 
to  the  finely  divided  Pt. 

Nos.  16,  18,  20,  and  23  were  treated  with  20  c.c.  HNO3  (1.20 
sp.  gr.),  boiled,  and  then  10  c.c.  more  added.  They  all  gave  tur- 
bid solutions  of  a  brownish  color. 

Nos.  17,  21,  and  24  were  treated  with  20  c.c.  HNO3  (1.16 
sp.  gr.),  boiled,  and  5  c.c.  more  added.  21  and  24  broke  up,  but 
17  did  not.  All  the  solutions  had  to  be  filtered,  the  residues  thor- 
oughly washed,  and  the  filters  and  contents  transferred  to  porce- 
lain crucibles,  ignited,  and  weighed. 

It  is  very  evident  from  the  results  in  Table  I  that  HNO3  will 
not  dissolve  in  one  treatment,  as  it  is  frequently  claimed  it  will, 
all  the  Pt  from  an  alloy  of  Ag  and  Pt. 

The  results  in  Table  II  show  the  effects  of  adding  gold  to 
an  alloy  of  silver  and  platinum  and  treating  the  button  with 
HN03  (1.28  sp.  gr.). 

All  the  tests  were  cupelled  near  the  front  of  a  gas-muffle  until 
near  the  blicking- point,  when  they  were  pushed  to  the  back  and 
kept  there  3  minutes  after  the  colors  had  disappeared. 

The  buttons  all  indicated  the  presence  of  Pt. 

No.  25  was  treated  with  25  c.c.  HNO3  (1.28  sp.  gr.)  and  kept 
warm  while  action  lasted,  and  then  boiled.  The  other  buttons 
were  treated  with  20  c.c.  hot  HNO3  (1.28  sp.  gr.),  boiled,  this  solu- 
tion decanted  and  10  c.c.  fresh  acid  added.  After  boiling  in  this 
the  residues  were  thoroughly  washed  and  transferred  to  porce- 


PLATINUM  AND   THE  PLATINUM  GROUP. 


235 


g 


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fl'f*  W 

111 

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0)   0) 

II 


I 


as 
ss 


in 


c? 


236 


NOTES  ON  ASSAYING. 


£ 


a 


Platinum 
Dissolved. 


Pt  +  Au 
put  in, 
rammes. 


SI 
- 


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00 

00 


to 

MM 


PLATINUM  AND   THE  PLATINUM  GROUP.  237 

lain  crucibles.  All  the  solutions  were  clear  and  there  was  no  more 
difficulty  in  collecting  the  residues  than  in  the  usual  parting  for 
gold. 

The  Pt  dissolved  was  considered  the  difference  between  the 
residue  left  after  parting  and  the  Au  +  Pt  originally  taken.  This- 
is  not  strictly  correct,  because  there  is  a  loss  of  gold  in  cupelling,, 
but  the  amount  of  Pt  found  in  the  cupels  was  practically  nothing^ 

It  will  be  seen  from  this  series  of  tests  that  gold  has  a  remark- 
able influence  upon  the  solubility  of  Pt  in  HNO3  when  alloyed 
with  silver,  and  its  presence  also  renders  the  solutions  clear  and 
residues  readily  handled. 

From  Table  II  the  best  ratio  seems  to  be  Pt  i,  Au  i  or  2^. 

AgiS- 

The  following  tables  seem  to  show  that,  even  with  this  ratio 
of  gold  and  silver  to  platinum,  three  treatments  with  HNO^ 
(1.28  sp.  gr.)  are  necessary  to  dissolve  all  the  Pt. 

One  more  cupellation  with  Ag  and  parting  in  acid  will  dis- 
solve all  the  Pt  and  leave  a  golden-yellow  residue.  All  the  buttons- 
were  cupelled  at  a  high  temperature  and  left  in  the  furnace  one 
minute  after  the  colors  had  disappeared.  The  parting  was  done 
by  dropping  them  in  25  c.c.  of  warm  HNO3,  boiling  the  solution 
after  action  had  ceased,  diluting  to  35  c.c.,  washing  and  filtering- 
The  filtering  was  simply  an  extra  precaution,  for  the  solutions  were 
clear  and  colorless.  On  the  other  hand,  if  silver  alone  is  used, 
a  great  many  partings  are  necessary,  the  solutions  are  turbid,, 
the  residues  are  extremely  finely  divided,  and  filtering  is  gener- 
ally necessary. 

The  presence  of  gold  increases  the  solubility  of  Pt  in  HNO^ 
and  the  per  cent  of  Pt  dissolved,  when  the  ratio  of  i  or  2  of  gold 
is  used,  is  always  high,  yet  it  varies  considerably,  which  seems  to 
indicate  that  there  is  some  factor  in  regard  to  its  solubility  yet 
undetermined.*  The  solutions  from  the  nitrations  were  freed 
from  silver  and  tested  for  gold,  but  none  was  found. 

The  loss  of  Pt  during  cupellation  is  very  small,  but  there  must 

*  Notes  on  the  Separation  of  Au,  Ag,  and  Pt,  Journ.  Soc.  Chem.  2nd.,  vol.  22,. 
p.  1324,  by  H.  Carmichael. 


238 


NOTES  ON  ASSAYING. 


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PLATINUM  AND  THE  PLATINUM  GROUP.  239 

be  a  loss  of  gold,  and  this  loss,  together  with  any  loss  in  parting, 
will  make  the  final  Pt  results  too  high. 

Too  high  results  for  Pt  and  other  rare  metals  may  also  be 
•obtained,  due  to  the  solubility  of  these  metals  in  acids  when  al- 
loyed with  each  other,  though  not  otherwise  soluble. 

Experiments  in  this  laboratory  by  Mr.  J.  R.  Marston  seem  to 
show  the  following: 

Alloys  of  Ag  and  any  of  the  Pt  group  must  be  rolled  or  ham- 
mered thin  before  treatment  with  any  acid.  When  H2SO4  is  used 
it  must  be  strong  and  the  button  must  be  boiled  in  it  for  some 
time,  otherwise  some  silver  will  remain  undissolved. 

To  treat,  the  residue  with  HNO3,  after  the  H2SO4,  is  not  always 
safe,  as  Pt  may  dissolve. 

Platinum. — According  to  my  experiments  when  an  alloy  of 
Pt  and  Pb  is  treated  even  with  dilute  HNO3  (i.i  or  1.2  sp.  gr.) 
an  appreciable  amount  of  Pt  goes  into  solution. 

The  residues  after  treatment  are  liable  to  adhere  to  both 
glazed  and  unglazed  cups. 

According  to  Winkler,*  when  an  alloy  of  Pb  and  Pt  is  treated 
with  HNO3,  13.11%  of  the  Pt  is  soluble  in  acid  of  1.19  sp.  gr.; 
13.23%  in  acid  of  1.298  sp.  gr.;  and  14.57%  in  acid  of  1.398 
sp.  gr. 

The  alloy  formed  seems  to  be  Pb2Pt  when  the  lead  is  in  ex- 
cess, and  PbPt  when  not. 

Gold  and  silver  alloy  perfectly  with  Pt;  other  metals  of  the 
group,  with  the  exception  of  palladium,  are  said  not  to  form  per- 
fect alloys. 

Iridium. — When  a  silver  button,  after  cupellation,  contains 
iridium,  the  surface  has  an  irregular  appearance,  similar  to  that 
.given  by  Pt,  but  the  roughness  seems  of  a  finer  texture. 

When  present  in  an  alloy  of  Ir+Pt  i  part,  Ag  12  to  15  parts, 
the  solubility  of  the  Pt  in  HNO3  is  diminished. 

It  seems  to  be  insoluble  in  dilute  aqua  regia,  and  only  slightly 
soluble  in  aqua  regia  made  up  of  i  HNO3  and  5  HC1  or  i  HNO3 
and  3  HC1.  The  presence  of  platinum  alone  seems  to  increase 

*  Solubility  of  the  Pt  in  Pt  alloys  in  HNO3,  Journ.  Chem.  Soc.,  vol.  13,  p.  428, 


240  NOTES  ON  ASSAYING. 

the  solubility  of  th?  iridium.     It  is  soluble  in  aqua  regia  of  i  part 
HNO3  and  2  parts  HC1. 

Ag  and  Ir,  melted  with  lead,  are  very  difficult  to  alloy,  the  Ir 
tending  to  float  and  resist  alloying.  Iridium,  in  an  alloy  of  Ir 
i  part,  Ag  12,  15,  or  18  parts,  is  partly  soluble  in  strong  H2SO4 
(1.84  sp.  gr.),  HNO3  (1.20  sp.  gr.),  and  HNO3  (1.28  sp.  gr.). 

When  the  ratio  is  Ir  i  part,  Ag  3  parts,  the  amount  dissolved 
in  the  same  acids  is  still  appreciable.  In  an  alloy  of  Au  and  Ir 
the  latter  tends  to  sink  to  the  bottom. 

Ferrous  sulphate,  oxalic  acid,  and  SO2  do  not  precipitate 
iridium  from  iridic  chloride. 

Palladium. — When  present  in  a  silver  button,  after  cupella- 
tion,  palladium  gives  the  surface  a  raised  or  embossed  appear- 
ance and  not  a  rough  and  pitted  one  like  Pt.  The  button  is 
brighter  than  when  Pt,  Ir,  or  both  Pt  and  Ir  are  present,  and 
does  not  stick  to  cupel.  Alloyed  with  lead,  some  Pd  is  soluble 
when  the  alloy  is  treated  with  acetic  acid.  Alloyed  with  silver, 
it  is  soluble  in  both  HNO3  and  strong  hot  H2SO4,  and  a  large  excess 
of  silver  tends  to  increase  the  solubility.  The  residue  after  treat- 
ment with  H2SO4  hangs  together  like  a  flocculent  precipitate. 

During  ordinary  cupellation  the  loss  of  Pt,  Ir,  Rh,  and  Pd  by 
volatilization  or  absorption  of  the  cupel  may  be  considered  as 
nothing. 

There  are  three  oxides:  Pd2O,  the  suboxide;  PdO,  mon- 
oxide; PdO2,  dioxide.  The  last  two  are  black. 

Osmium. — This  is  supposed  to  oxidize  completely  to  OsO4 
during  cupellation  and  to  volatilize.  If  present  in  small  amount, 
it  may  do  so;  if  in  large  amount,  it  will  not.  The  vapors  are  very- 
poisonous.  If  Os,  Ag,  and  Pb  are  placed  on  a  cupel,  owing 
to  the  infusibility  of  Os  it  floats  on  the  AgPb  alloy  and  oxidizes. 
During  this  oxidation,  if  the  temperature  is  above  that  of  the 
formation  of  PbO  crystals,  portions  of  the  alloy  will  be  thrown 
off  and  the  cupel  will  be  covered  with  small  beads  of  Ag.  If 
PbO  crystals  are  forming,  it  is  difficult  to  keep  the  alloy  driving.. 

If  the  Os  does  not  completely  volatilize,  near  the  blicking- 
point  black  spots  appear  on  the  Ag  bead,  which  flash  off  and  on,. 


PLATINUM  AND   THE  PLATINUM  GROUP. 


241 


but  finally  disappear  when  the  button  brightens.  Such  buttons 
are  liable  to  sprout,  appear  rough  on  the  surface,  and  are  not  so 
bright  as  a  Ag  bead.  In  HNO3,  OsO4  is  formed. 

When  cupelling  a  button  containing  Os  do  not,  at  the  same 
time,  cupel  any  buttons  containing  iridium. 

CUPELLATION   OF   OS,   AG,   AND   Pl3. 


Parted  in 

Weight 

Percent- 

Os. 

Ag, 

Per  Cent 

Lead, 

H2SO4, 

after 

Loss, 

age 

Grammes. 

Grammes. 

Os. 

Grammes. 

Specific 

Parting, 

Grammes. 

Os 

Gravity. 

Grammes. 

Lost. 

.00491 

.5000 

1.  00 

6 

1.84 

.00219 

.00272 

55-4 

.00392 

.5000 

1.  00 

20 

'  ' 

.00100 

.00292 

74-5 

.00517 

.2500 

2.00 

6 

M 

.00100 

.00417 

80.6 

.00565 

.2500 

2.00 

20 

.  00085 

.  00480 

84.9 

The  H2SO4  must  be  strong  and  thoroughly  boiled  to  remove 
the  Ag.  The  residue  is  fine  and  black. 

Ruthenium. — Less  fusible  than  rhodium,  but  more  fusible 
than  osmium. 

There  are  three  oxides:  RuO,  RuO2,  and  Ru2O3.  RuO 
and  RuO2  are  volatile,  but  not  so  easily  as  OsO4.  Ru2O3  is 
bluish  black  and  is  formed  when  the  metal  is  ignited  in  the 
air. 

When  much  Ru  is  present  in  a  lead-silver  alloy,  if  the  lead 
drives,  a  black  film  soon  appears  and  will  be  left  on  the  button, 
when  near  the  blicking  point.  A  black  scum  will  also  be  left 
on  the  cupel  together  with  small  silver  beads,  as  in  the  case 
of  Os.  If  a  small  amount  is  present,  the  button  while  driving 
appears  more  or  less  irregular,  with  spots  over  the  surface.  At 
the  end  it  rounds  up  slightly,  a  partial  play  of  colors  will  be 
noticed,  it  then  flattens  and  sets. 

The  surface  of  the  silver  button  may  be  all  bluish  black  or 
there  may  be  black  spots  (RuO2  or  Ru2O3)  on  a  silvery  surface. 
If  only  a  little  Ru  is  left,  the  surface  is  bright  but  rough  and 
covered  with  bright  silvery  plates. 

Owing  to  the  black  oxide  left  on  the  beads,  it  is  difficult  to 
determine  the  loss  of  Ru  during  cupellation,  but  experiments 


242  NOTES  ON  ASSAYING. 

carried  out  on  the  same  line  as  the  table  under  osmium  seem 
to  show  that  20%  to  45%  of  the  Ru  may  volatilize. 

Iridosmium. — Experiments  on  this  have  not  been  satisfactory, 
owing  to  the  difficulty  of  obtaining  it  perfectly  free  from  other 
members  of  the  group. 

The  presence  of  ten  per  cent  in  a  silver  bead  will  give  that 
bead  an  unusually  bright  appearance  and  make  it  look  as  though 
it  was  covered  with  bright,  flat,  silvery  plates  or  crystals. 


METALLURGICAL  LABORATORY 
EXPERIMENTS  AND  NOTES. 

FOURTH  YEAR. 

GENERAL    DIRECTIONS. 

WHEN  performing  on  a  small  scale  any  of  the  experiments 
described,  it  will  be  well  for  students  to  observe  the  following 
precautions: 

1.  When   several  students  are  working  upon  the  same  ore, 
only  one  student  at  a  time  should  sample  it. 

2.  In  order  to  prevent  resampling  the  ore,  should  anything 
happen  to  the  experiment,  always  take  two  or  more  times  the 
amount  of  ore  called  for  in  the  experiment. 

3.  Save  the  original  ore  sample  and  any  products  that  may 
result  from  the  work  until  all  results  are  figured  out  and  the 
report  completed. 

4.  Save  all  solutions,  filtrates,  concentrates,  and  any  prod- 
uct  relating  to   the  test  or  experiment  until  the  report  is  com- 
pleted. 

5.  If   any  ore   or  product  contains   lumps    after   treatment, 
always  pass  it  through  a  sieve  a  little  coarser  than  the  ore  went 
through  before  treatment,  then  mix  thoroughly  and  sample. 

6.  Try  in  every  possible  way  to  avoid  repeating  any  part  of 
your  work. 

Solutions. — These  are  made  up: 
ist.  By  dissolving  a  solid  in  a  liquid. 
2d.  By  adding  one  liquid  to  another. 

Jn  these  notes  all  solutions  are  made  up  in  the  following  way: 

243 


244  NOTES   ON  ASSAYING. 

A  1%  cyanide  solution  means  that  a  ton  of  water  contains 
1995  Ibs.  of  water  and  5  Ibs.  of  KCy,  or  that  500  c.c.  of  a  J% 
solution  contains  498.75  c.c.  of  water  and  1.25  grammes  of  KCy. 

If  we  wish  to  make  up  a  J%  solution  of  H2SO4  and  the 
H2SO4  has  a  sp.  gr.  of  1.82,  we  take  1990  Ibs.  of  water  and  10 
Ibs.  of  acid,  or  we  can  take  1990  c.c.  of  water  and  5.49  c.c. 

of  acid- 


If  we  treat  300  grammes  of  ore  with  70  per  cent  01  water, 
3  per  cent  of  H2SO4,  and  ij  per  cent  of  bleaching-powder,  we  use: 

Ore  ...........................   300  grammes 

Water  .........................   210         " 

Bleach  ......................  ...     4J 

H2S04  .........................     9          "  or*£ 

=  4.9  c.c.,  which  can  be  measured  in  a  small  graduate. 

CALCINING. 

In  these  notes  calcining  means  the  heating  of  a  substance  out 
of  contact  with  the  air.  Roasting  is  the  heating  of  a  substance 
with  access  of  air. 

Examples  of  calcining  are: 

1.  Heating  an  ore  like  limonite  or  gothite  to  drive  off  its  water. 

2.  Heating  limestone  in  a  retort  or  crucible;  the  CO2  is  driven 
off  and  CaO  is  left. 

3.  Heating  a  rock  to  make  it  more  porous  or  friable. 

In  the  first  two  cases,  the  substances  at  the  end  of  the  roast  are 
different  from  those  at  the  beginning,  but  heat  alone  has  effected 
the  change.  In  the  last  case  no  chemical  change  has  taken  place. 

ROASTING. 

We  have  several  methods,  and  at  the  end  of  the  roast  the  sub- 
stances with  which  we  started  have  generally  undergone  a  change. 

Oxidizing  roast  is  where  we  roast  with  full  access  of  air.  If 
an  ore  is  FeS2,  the  reaction  will  be 

2FeS2+  nO  =  Fe2O3+4SO2. 


METALLURGICAL   LABORATORY  EXPERIMENTS.  245 

We  lose  4  parts  of  sulphur  =  128,  and  we  gain  30  =  48,  that  is, 
we  lose  80  parts.  We  start  with  2FeS2=24o  parts;  therefore  we 
lose  33  per  cent. 

In  this  roast  we  may  have  Fe3O4  formed,  as  well  as  Fe2O3,  for 
if  two  roasting  dishes  containing  FeS2  are  placed  in  the  same 
muffle,  one  behind  the  other,  the  front  one  will  receive  more 
air  than  the  back  one,  and  the  iron  in  the  front  one  will  probably 
exist  as  Fe2O3  at  the  end  of  the  roast,  whereas  in  the  back  one 
there  is  liable  to  be  considerable  Fe3O4  present. 

Sulphatizing  Roast.  —  This  is  where  we  try  to  form  sulphates. 
The  SO2  in  the  oxidizing  roast  can  further  oxidize  to  SO3,  and 
this  can  combine  with  any  FeO  or  CuO  in  the  ore  and  form 
FeSO4  or  CuSO4.  As2O3  may  also  oxidize  further  and  form 
As2O5,  or  we  may  have  3FeO  +  As2O3  =  Fe3As2O6.  The  Ziervogel 
Process,  where  the  aim  is  to  form  Ag2SO4,  is  a  well-known  example 
of  this  kind  of  roast. 

Chloridizing  Roast.  —  In  this  roast  salt  is  added  to  the  ore  and 
the  object  is  to  form  sulphates  as  in  the  sulphatizing  roast,  some 
of  which  decompose  the  salt,  thus  chloridizing  the  ore.  The  salt 
may  be  added  at  the  beginning,  at  the  end,  or  during  the  roast. 
Silver  ores  for  amalgamation  or  lixiviation  are  treated  in  this  way. 

Roasting  and  Reaction  Process.  —  This  takes  place  in  one 
Idnd  of  lead  smelting.  The  PbS  is  partly  roasted  to  form  PbSO4 
and  PbO.  These  then  act  on  the  PbS  still  unchanged  and  we 
have  PbS  +  PbSO4  =  2Pb+2SO2; 


CHLORINATION   OF   GOLD   ORES. 

Plattner  Process  of  Chlorination.  —  This  method  for  the  extrac- 
tion of  gold  is  applicable  to  some  ores  in  a  raw  condition,  but  is 
especially  suited  for  the  treatment  of  sulphide  concentrates  from 
stamp-mills,  the  free  gold  having  previously  been  extracted. 
Coarse  gold  is  only  sbv/ly  acted  upon  by  chlorine  gas. 

Experiment.  —  Pulverize  the  ore  through  4o-mesh  sieve,  sample 
•carefully,  grind  sample  through  100-  or  i2o-mesh  sieve,  and  assay. 

Take  300  grammes  of  ore  (through  40),  and  roast  dead  in  an 
iron  pan  or  clay  dish  (6"  clay  dish  will  hold  from  125  to  225 


246  NOTES  ON  ASSAYING. 

grammes).  It  is  better  to  roast  two  portions  of  125  than  one 
portion  of  250,  for  the  ore  in  the  latter  case  is  apt  to  be  too  deep. 

Roast  at  a  very  low  heat  at  first  to  prevent  caking  (the  larger 
the  amount  of  sulphides  the  lower  the  heat),  and  then  increase  to 
a  high  temperature,  stirring  frequently. 

At  high  temperatures  iron  and  copper  sulphate  are  both 
decomposed : 

2FeSO4  =  Fe2O3+SO2+SO3  and  CuSO4  =  CuO  +  SO2-{-O. 

The  basic  iron  sulphate  is  only  decomposed  at  a  very  high 
temperature.  In  a  dead  roast  neither  sulphates  nor  sulphides 
are  present.  If  there  is  any  doubt  about  the  roast  being  dead,, 
remove  the  dish  from  the  muffle,  add  some  fine  charcoal,  stir 
well,  put  back  in  the  muffle  and  roast  again,  but  do  not  stir  at 
first  in  order  to  allow  the  charcoal  to  burn.  Repeat  this,  adding 
the  charcoal  when  the  dish  is  outside  the  furnace,  until  no  odor 
of  SO2  is  detected. 

Ores  containing  arsenic  are  especially  difficult  to  roast  dead,, 
and  the  addition  of  charcoal  is  very  beneficial.  The  charcoal 
reduces  the  sulphates  to  sulphides,  and  arseniates  to  arsenides,, 
which  are  then  broken  up  with  the  liberation  of  SO2  and  As2O3. 
In  practice  it  is  not  used  in  roasting,  the  sulphates  being  broken, 
up  by  heat  alone.  At  the  completion  of  the  roast,  the  gold  is  in. 
a  metallic  condition  and  all  other  metals  exist  as  oxides,  with  the 
exception  of  metals  like  lime,  lead,  and  zinc,  which  may  be  present 
as  sulphates.  Any  ferrous  sulphate  not  decomposed  would  be 
oxidized  by  the  Cl  gas  to  ferric  sulphate  and  would  do  no  harm 
(6Fe$O4+3Cl2  =  2Fe2(SO4)3+Fe2Cl6),  but  the  consumption  of 
chemicals  would  of  course  be  increased. 

Any  sulphides  or  charcoal  left  in  the  ore  would  be  harmful,, 
as  they  would  precipitate  the  gold  from  the  AuCl3: 

2AuCl3+3CuS  =  Au2S3+3CuCl2,     or 
3CuS+8AuCl3+  i2H2O  =  8Au+  24HCl+3CuSO4; 
4AuCl3+  30  -f  6H2O  =  4Au+ 1 2HC1+  3CO2. 

Sift  the  ore  through  a  3o-mesh  sieve  to  remove  any  scales, 
ami  break  up  any  lumps.  WEIGH,  sample,  and  grind  sample  for 
assay  as  fine  as  law  ore  sample  for  assay. 


METALLURGICAL  LABORATORY  EXPERIMENTS. 


247 


Chlorinate  the  remainder  in  the  following  manner: 

MnO2 3    parts  or  24  gm. 

NaCl 4      "      "32gm. 

H2SO4 loj     "     "  84  c.c.  (commercial  acid) 

H20 7      "     "  s6c.c. 

Clamp. 

"--—  Cover,  (d) 

—Groove  for  rubber  gask«L 


Ore 


Hz  O  to  wash  Cl.  . 
and  give  the  rate  of 
ow  of  the  gas. 


Fine  quarts 
Coarse  « 


By  adding  the  H2O+H2SO4  gradually,  the  above  will  run 
about  i|-  hours.  At  the  Utica  Mine,  CaL,  the  proportions  used 
are  90  Ibs.  MnO2,  100  Ibs.  salt,  and  200  Ibs.  H2SO4. 

Reactions: 


2NaCl+  H2S04  =  2 

MnO2+4HCl  =  MnCl2+2H2O-f  2C1; 

MnCl2+H2S04=MnSO4+  2HC1. 

Before  placing  the  ore  in  bottle  At  fill  it  with  water  and  see  that 
it  does  not  leak  around  the  hole  o  and  the  tube  x. 

Moisten  the  ore  slightly  with  from  6  to  20%  of  water  (if 
lime  is  present,  moisten  with  dilute  H-jSOJ  and  then  shake  lightly 
into  bottle  A,  which  it  should  not  fill  more  than  two  thirds  (200 
grammes  will  go  nicely  in  a  pint  jar).  Dry  chlorine  has  very 
little  action  upon  gold.  The  cover  (d)  is  next  put  on  lightly  to 
allow  the  Cl  to  come  through;  connect  tubes  oc  and  z  and  pass 
chlorine  gas  through  the  ore  for  i  to  ij  hours,  after  it  is  noticed 
coming  from  beneath  cover  (d).  Keep  a  vessel  of  ammonia  near, 
to  from  NH4C1.  Then  fill  groove  (e)  with  water,  put  in  rubber 
gasket,  clamp  cover  on  tightly,  and  pass  in  Cl  for  5  minutes 


248  NOTES  ON  ASSAYING. 

longer.  Disconnect  at  (y),  stop  tube  up  with  a  piece  of  glass  rod 
and  allow  jar  to  stand  at  least  96  hours,  at  the  end  of  which  time 
the  jar  should  be  full  of  gas.  The  gold  should  then  be  in  the 
condition  of  AuCl3. 

Most  sulphides  and  FeS2  are  attacked  by  chlorine  (R2S+8C1+ 
4H2O  =  R2SO4+8HC1),  while  most  peroxides  and  ferric  oxide  are 
not.  When  cover  (d)  is  removed  a  strong  odor  of  chlorine  should 
be  noticed.  Leach  the  ore  with  as  little  cold  water  as  possible  to 
avoid  dissolving  any  more  foreign  salts  than  is  necessary.  It  can 
be  done  either  by  forcing  water  up  through  tube  (x)  until  it  rises 
above  the  ore,  or  by  pouring  water  on  the  ore  until  it  just  covers  it. 
Allow  to  stand  15  minutes  and  draw  off  at  (x).  Repeat  three 
times  more  or  until  a  portion  of  the  nitrate  tested  with  FeSO4 
gives  no  purple  cloud  (gold).  If  the  first  leaching  water  is  pink 
it  indicates  the  presence  of  manganese  in  the  ore,  which  has  been 
oxidized  with  the  formation  of  some  permanganate  salt.  The 
main  body  of  the  filtrate  should  be  kept  separate  from  the  portions 
which  have  been  tested  with  FeSO^.  Save  all  the  portions.  Evap- 
orate the  main  solution  to  about  300  c.c.  to  drive  off  the  chlorine. 
If  the  solution  is  clear,  add  the  portions  of  AuCl3  solution  containing 
FeSO4  and  a  little  fresh  FeSO4.  If  it  is  not  clear,  add  a  few  drops 
of  HC1;  if  this  does  not  clear  it  or  there  is  much  residue,  filter. 
The  filter  and  contents  should  be  saved  and  assayed  if  there 
is  any  likelihood  of  its  containing  gold.  To  the  hot  filtrate  add 
the  portions  of  AuCl3  solution  containing  FeSO4  and  a  little 
fresh  FeSO4: 

2AuCl3+  6FeSO4  =  2  Au+  Fe2Cl6+  2Fe2(SO4)3. 
If  the  original  ore  contained  arsenic,  we  might  obtain  here  a 
whitish  precipitate  of  ferrous  arseniate,  but  the  HC1  should  keep 
this  in  solution. 

Allow  to  stand  at  least  forty-eight  hours  and  then  filter  on  a 
small  filter.  Save  this  filtrate,  add  a  little  fresh  FeSO4,  and  allow 
to  stand  twenty-four  hours  more  to  see  whether  all  the  gold  has 
come  down.  The  moist  filter  and  contents  are  wrapped  in 
10  grammes  of  C.P.  lead,  to  which  has  been  added  three  times 
as  much  C.P.  silver  as  there  is  gold  in  the  total  amount  of  ore 
chlorinated. 

A  hot  cupel  is  brought  to  the  front  of  the  muffle  and  the  lead 
and  its  contents  dropped  into  it.  Allow  the  filter  to  burn  slowly 


METALLURGICAL   LABORATORY  EXPERIMENTS. 


249 


and  gradually,  pushing  the  cupel  back  into  the  muffle  until  the 
lead  begins  to  drive.  If  it  does  not  drive,  add  more  lead.  When 
the  button  is  driving  tip  the  cupel  slightly  in  all  directions,  in 
'Order  to  collect  any  minute  globules  and  filter- ash  on  the  inner 
surface  of  the  cupel.  Cupel  as  usual,  part  the  resulting  silver  and 
gold  bead,  and  weigh  the  gold. 

After  the  extraction  of  the  AuCl3,  >  the  ore  together  with  the 
filter  is  emptied  from  the  bottle  into  some  vessel,  is  dried,  sifted 
from  the  filter  of  quartz  (a  little  quartz  in  the  ore  will  not  matter), 
WEIGHED,  sampled,  a  sample  put  through  the  same  mesh  sieve 
as  the  sample  of  the  raw  ore  used  for  assay,  and  valued. 

Students  should  obtain  all  the  data  given  below  and  should 
hand  in  a  report  similar  to  the  following: 

Number  and  character  of  the  ore. 

Length  of  roast  and  how  conducted. 

Length  of  time  of  passage  of  chlorine  through  the  ore,  time  of 
contact  with  it,  and  whether  present  on  opening  jar. 

Manner  of  leaching  and  time. 

Precipitant  used,  i.e.,  whether  FeSO4,  H2S,  or  some  other. 

Base  all  the  following  results  on  the  raw  ore  or  the  ore  that  you 
started  with  and  the  gold  in  it. 

In  columns  3  and  4  carry  out  figures  to  four  places  of  deci- 
mals; if  next  figure  is  5  or  more,  increase  the  preceding  figure 
by  one. 


i 
Weight. 

2 

Assay 
per  Ton. 

Weight  of 
Gold  in 
Grammes. 

4 
Percentage  of  Gold 
Lost  in  Roast. 

Raw  ore  

coo  gms 

54.    OZ 

0926 

Roasted  ore 

4.7C       '« 

r    6      " 

.OOI4_ 

.0926               X' 

Ore  actually  chlorinated  =381  grammes. 

Ore  after  leaching  with  water=38o  grammes.     Assay  per  ton=.4  oz. 
Gold  in  tailings  (29.166  :  380  : :  .0004  :  #)  =  .oo52  grammes. 
If  we  had  chlorinated  475  grammes  of  ore,  the  tailings  would  have  been  473 
.grammes;   therefore  the  gold  in  the  tailings  from  475  grammes 
(29.166  :  473  :  :  .0004  :  #)  =  .oo65  grammes. 

Gold  actually  recovered  by  chlorination  from  381  grammes  =  .0677  grammes 
Gold  recovered,  based  on  475         "        =.0844         " 

' 


250  NOTES  ON  ASSAYING. 

The  following  tables  should  always  be  added: 

Table  I.  Table  II. 

Percentage  of  gold  lost  during  roast  .1.51%  .1.51%. 

"     "       "  in  tailings...    '7.02%  7.02% 

"     "     saved  (actually)  .  91  .  14%  (Based  on  tailings  assay)    91.47% 

99.67%  100.00% 

On  Nova  Scotia  concentrates  it  sometimes  seems  advisable 
to  add  H2SO4  to  the  AuCl3  solution  in  preference  to  HC1,  but 
ferrous  arsenate  and  arsenite  are  both  more  soluble  in  HC1  than 
in  H2SO4. 

The  gold  could  also  be  precipitated  from  an  AuCL,  solution 
by  hydrosulphuric  acid,  sulphurous  acid,  by  a  metallic  sulphide, 
by  charcoal  or  by  oxalic  acid. 

Hydrosulphuric  acid  throws  down  Au2S2  from  a  cold  solution  : 

2  AuCl3  +  3H2S  =  Au2S2  +  S  +  6HC1. 

When  the  solution  is  hot,  Au2S2,  Au2S3,  and  metallic  gold  all 
come  down. 

When  SO2  or  a  metallic  sulphide  are  used  we  have 
2AuCl,+  3S02+  6H20  =  2Au+  6HC1+  3H2SO4; 


Where  charcoal  is  used  as  a  precipitant,  Mr.  W.  M.  Davis, 
the  inventor,  claimed  that  the  reaction  which  takes  place  is 
4AuCl3+3C+6H2O  =  4Au+i2HCl+3CO2,  but  it  seems  probable 
that  the  following  also  occur: 

6H2S04+  3C  -  6H20  +  6SO2+  3CO2  ; 


Aluminium-foil  may  also  be  successfully  used  in  the  laboratory. 

In  practice  the  gold  and  impurities  thrown  down  by  FeSO4 
or  H2S  are  filtered,  and  if  many  impurities  are  present  the  whole 
material  is  either  roasted  at  a  very,  very  low  heal,  to  drive  off  the 
arsenic  and  other  volatile  compounds,  or  else  boiled  with  H2SO4 
or  HC1  to  remove  arsenic,  iron,  and  any  soluble  substances.  It 
is  then  dried  and  smelted  in  a  graphite  crucible  with  borax  glass 
and  a  little  soda,  and  towards  the  end  of  the  operation  a  little  nitre. 

Borax  glass  may  bs  replaced  by  SiO2,  i.e.,  the  slag  must  be 
acid  so  that  iron  will  not  go  into  the  bullion.  The  slag  is  skimmed 
off  and  the  gold  poured  into  a  very  hot  mould  which  has  been 
oiled  or  into  which  fine  rosin  has  been  sprinkled. 


METALLURGICAL   LABORATORY  EXPERIMENTS. 


Formerly  the  excess  of  chlorine  in  the  AuCl3  solution  was 
neutralized  by  passing  SO2  gas  into  it,  but  it  is  now  found 
better  to  neutralize  with  FeSO4  which  is  oxidized  to  the  higher 
sulphate. 

Liquid  chlorine,  which  comes  in  tanks  holding  about  130  Ibs.,, 
is  used  in  some  works,  and  i  to  2  Ibs.,  it  is  said,  will  chlorinate 
a  ton  of  well- roasted  ore. 

The  FeSO4  solution  should  be  clear  and  light  green  in  color. 
It  can  always  be  kept  in  this  condition  by  dissolving  the  salt  in 
H2O,  filtering,  and  transferring  the  solution  to  a  bottle.  Now 
add  a  piece  of  iron  and  a  little  H2SO4,  so  that  hydrogen  will  be 
given  off  continually.  A  stopper  is  now  placed  in  the 
arranged  as  per  sketch,  which  allows 
the  hydrogen  to  escape,  but  no  air 
to  enter. 

When  you  wish  any  of  the 
solution  do  not  try  to  pour  from 
opening  (c),  but  remove  the  stopper. 

Effect  of  Impurities  upon  the 
Precipitation  of  Gold  from  AuCl3. — 
The  following  experiments  were 
carried  out  by  Mr.  A.  L.  Hamilton, 
class  of  1900: 

Two  solutions  of  AuCl3  were 
used,  one  containing,  per  200  c.c. 
of  solution,  .01087  grammes  of  gold, 
the  other  .01120  grammes.  These 
values  were  obtained  by  three 
methods,  throwing  down  the  gold 
from  200  c.c.  of  solution  by  means 
of  FeSO4  and  H2S  and  evaporating 
200  c.c.  with  litharge.  In  the 
experiments  the  required  percent- 
ages of  the  chlorides  of  copper, 
lime,  and  magnesia  were  weighed, 
placed  in  beakers,  and  then  dis- 


a,  glass  plug;  b,  rubber  tube; 
c,  slit  in  rubber  tube;  d,  glass 
tube  open  at  both  ends;  e, 
stopper;  /,  iron  nail. 


solved  in  200  c.c.  of  the  gold  chloride  solution.     In  the  case  of 


252 


NOTES  ON  ASSAYING. 


arsenic,  arseniate  of  soda  was  used  and   the  solution  was  made 
acid  with  H2SO4  before  the  addition  of  the  FeSO4. 

The  following  table  will  give  the  results  of  the  tests  in  a  con- 
densed form: 


Per 
Cent 
•of  Ca 
in 
Solu- 
tion. 

Gold 
not 
Precip- 
itated, 
Per 
Cent. 

Time 
of 
Precip- 
itation, 
Hours. 

Per 
Cent 

of  Mg 
in 
Solu- 
tion. 

Gold 
not 
Precip- 
itated, 
Per 
Cent. 

Time, 
Hours. 

Per 
Cent 
of  Ar- 
senic. 

Gold 

not 
Thrown 
Down, 
Per 
Cent. 

Time, 
Hours. 

Per 
Cent 

of 
Copper. 

Gold 
not 
Precip- 
itated, 
Per 
Cent. 

.09 

.297 

II5 

.012 

1.38 

120 

.017 

1.07 

300 

.002 

.276 

.18 

.644 

.029 

1.32 

•045 

2.8l 

.004 

.276 

•36 

•5°7 

.058 

1.25 

.088 

4.64 

.Oil 

.460 

.90 

6.58 

.117 

I.  II 

•265 

9.46 

.019 

.276 

1.  80 

6.08 

•234 

.67 

•443 

10.27 

.03 

.276 

3.60 

6.00 

.585 

.80 

.885 

II  .61 

I.I7 

.98 

1.77 

12.46 

All  the  above  results  are  in  each  case  the  average  of  two  experi- 
ments. In  the  tests  where  lime,  magnesia,  and  arsenic  were 
present  FeSO4  was  used  as  a  precipitant;  where  copper  was  pres- 
ent H2S  was  used. 

A  small  amount  of  copper  seems  to  have  very  little  effect  either 
when  H2S  or  FeSO4  is  used.  A  small  amount  of  magnesia  seems 
to  be  a  detriment,  and  arsenic  a  great  detriment.  In  the  case 
of  lime,  •  anything  above  .5%  appears  to  be  harmful.  To  see 
whether  CaSO4  would  drag  gold  down  from  a  chloride  solution 
the  following  tests  were  made: 

AuCl3  solution 200  c.c. 

Gold  contents 01120  grammes. 

Solutions  stood  250  hours. 


Grammes  CaCl2. 

Percentage  of  Ca 
in  the  Solution. 

Cubic  Centimetres 
of  H2S04  added. 

Gold  Recovered  from  the 
CaSO4.     Average  of 
two  tests. 

.2 

•°3 

2 

.'00004  grammes 

I.O 
2.0 

.18 
.36 

8 

.  00005           ' 
.  00008 

5 
10 

20 

.90 
1.  80 
3.60 

10 

15 
25 

.  00004           ' 
.00008 
.  00009           ' 

Barrel  Process  of  Chlorination. — Gold  ores  which  have  been 
roasted,  in  order  to  free  them  of  sulphur,  arsenic,  and  similar 


METALLURGICAL   LABORATORY  EXPERIMENTS.  253 

impurities,   may  be   chlorinated  by   this  process,    in   which   the 
chlorine  is  generated  by  means  of  bleaching-powder  and  H2SO4. 

Laboratory  tests  may  be  successfully  carried  out  as  follows: 

Experiment. — Sample  and  assay  the  original  ore;  if  it  is  raw, 
roast  it  as  described  under  the  Plattner  Process.  Take  a  pint 
or  quart  fruit- jar  having  a  glass  cover  and  rubber  gasket,  and 
test  it  with  bleach  and  H2SO4  to  see  whether  it  is  tight.  If  so, 
put  some  water  (equal  in  weight  to  at  least  70%  of  the  roasted 
ore  taken  for  chlorination)  in  the  jar.  Now  take  75  or  more 
grammes  of  roasted  ore  (through  a  30-  or  4o-mesh  sieve)  and  mix: 
it  with  the  specified  amount  (see  bulletin-board)  of  bleach,  pass  the 
whole  through  a  2o-mesh  sieve  to  remove  any  lumps,  and  pour 
the  mixture  into  the  jar.  The  object  of  this  is  to  prevent  the 
balling  up  of  the  bleach  and  the  formation  of  CaSO4  on  the  out- 
side of  the  lumps  and  hence  a  loss  of  bleach,  when  the  H2SO4  is 
added.  Add  the  specified  amount  of  H2SO4  and  stopper  the  jar 
quickly  and  tightly  by  means  of  the  glass  cover  and  rubber  gasket 
or  with  a  solid  rubber  stopper  and  a  large  iron  washer  between  the. 
rubber  stopper  and  the  spring  clamp.  Wrap  the  jar  in  a  cloth 
or  towel,  in  case  it  should  break,  shake  easily  and  gently,  and 
then  rotate  in  the  laboratory  apparatus  jor  the  required  length 
of  time.  The  contents  of  the  jar  should  be  of  the  consistency  of 
thin  mud,  and  the  amount  of  water  depends  both  upon  the  charac- 
ter of  the  ore  and  the  amount  of  H2SO4  and  bleach  used.  The 
amount  of  these  depends  upon  the  character  of  the  ore  and  the 
impurities  in  it,  which  have  to  be  converted  into  chlorides  and 
sulphates. 

The  acid  is  generally  ij  to  2  times  the  weight  of  the  bleaching- 
powder  used.  When  the  jar,  vessel,  or  barrel  has  been  revolved 
the  required  length  of  time  it  is  opened,  when  it  should  smell  very 
strongly  of  chlorine.  Fill  jar  with  water,  stir  well,  and  allow  to 
stand  15  minutes;  decant  solution,  cover  the  ore  with  H2O,  allow 
to  stand,  again  decant  and  then  throw  contents  on  a  large  filter, 
allow  to  drain,  cover  contents  of  filter  with  water,  again  allow  to 
drain,  and  repeat  twice  more  or  until  a  concentrated  solution  of 
FeSO4  gives  no  test  for  gold  when  added  to  the  filtrate  and 
allowed  to  stand  some  time. 

The  main  body  of  the  filtrate  should   be  kept  separate  from 


254  NOTES  ON  ASSAYING. 

the  portions  which  have  been  tested  with  FeSO4.  Save  all  the 
portions.  Besides  the  AuQ3,  the  nitrate  contains  sulphates  sol- 
uble in  water  and  possibly  some  free  H2SO4.  Evaporate  the  solu- 
tion to  350  or  400  c.c.j  but  remember  that  CaSO4  is  less  soluble  in 
liot  H2O  than  it  is  in  cold ;  therefore,  if  the  filtrate  is  heated  .and 
•evaporated  too  far,  CaSO4  will  separate  out.  This  can  be  dis- 
solved in  HC1,  but  if  we  have  HC1  and  H2SO4  both  present  in  the 
solution,  the  gold  will  not  wholly  come  down. 

Therefore,  if  CaSO4  does  come  down,  we  must  either  filter 
it  off  (save  filter  and  contents)  before  adding  the  FeSO4,  or 
evaporate  the  whole  solution  down  so  far  in  a  casserole  or  evapo- 
rating-dish  that  when  40  grammes  of  litharge  and  2  grammes  of 
.silica  are  added  the  mass  will  be  dry  and  granular.  Then  make 
.a  regular  fusion  of  the  whole  residue  in  a  crucible  glazed  on  the 
inside.  Cupel  the  lead  button,  after  the  addition  of  silver,  and 
part  the  resulting  silver  and  gold  bead  for  gold.  If  the  AuCl3 
solution  is  filtered,  the  filtrate  is  treated  as  per  Plattner  Process, 
commencing,  "To  the  filtrate  add,"  etc.  (page  248). 

Place  the  filter  and  contents  (ore  after  leaching)  in  a  roasting- 
•dish  and  burn  the  filter  in  a  muffb,  pass  the  whole  dry  material 
through  a  20-mesh  sieve,  to  remove  any  lumps,  WEIGH,  sample, 
crush  sample  through  same  sieve  as  the  original  sample  for  assay, 
and  value.  From  these  data  and  the  weight  and  assay  of  the  ore 
used,  calculate  the  percentage  of  gold  extracted  and  other  data  as 
per  example  under  Plattner  Process.  Give  in  fall  all  the  data 
possible  connected  with  the  experiment,  and  make  out  a  report 
similar  to  that  under  Plattner  Process  (pages  249  and  250). 

Of  course  the  whole  object  of  the  experiments  on  any  ore  is 
to  convert  the  gold  into  AuCl3,  and  have  the  consumption  of 
chemicals  small,  and  the  time  consumed  in  treatment  as  short  as 
possible.  A  silicious  ore,  for  instance,  would  consume  no  chlorine, 
while  a  calcareous  ore  would  consume  a  great  deal.  For  this 
reason  a  little  salt  is  often  added  to  the  ore  just  previous  to  its 
being  discharged  from  the  roasting-furnace.  In  some  laboratory 
tests  I  have  found  it  necessary  to  add  6  per  cent  H2SO4  and  10 
per  cent  of  bleach  before  a  successful  chlorination  was  obtained. 
These  higli  percentages  would,  of  course,  be  prohibitory  in  practice. 

In  some  ores  better  results  seem  to  be  obtained  by  adding  all 


METALLURGICAL   LABORATORY  EXPERIMENTS. 


255 


the  acid  and  bleaching-powder  at  one  time  and  then  rotating  the 
vessel;  in  others,  by  adding  part  of  the  chemicals,  rotating  for 
some  hours,  and  then  adding  the  remainder  of  trie  chemicals  and 
rotating  again. 

In  some  works  water  is  added  first,  then  the  acid,  and  lastly 
the  bleach;  in  others,  the  H2SO4  and  water  are  first  charged,  then 
the  ore,  and  lastly  the  bleach;  still  others  add  the  water,  bleach, 
ore,  and  lastly  the  acid. 

The  water  used  for  washing  is  generally  3000  to  5000  Ibs. 
per  ton  of  ore  treated. 

Bleaching-powder,  when  fresh,  contains  from  25  to  37%  avail- 
able chlorine,  and  it  should  be  kept  in  a  cool,  dry  place,  for  if 
it  becomes  moist  it  is  worthless: 

CaCl2O2+  CaCl2+  2H2SO4  =  2CaSO4+  2H2O+  2CL,. 
Remsen  gives  these  reactions: 

Ca(C10)2+H2S04  =  CaS04+  2HC1O; 
CaCl2+  H2S04  =  CaS04+  2HC1; 
2HC1+  2HC1O  =  2H2O+  2CL,. 

The  proportion  of  chemicals  and  ore  formerly  used  in  some 
large  works  is  as  follows: 


Ore, 

H2SO4, 

Bleach, 

H2O, 

Approx- 
imate 

Ton. 

Pounds. 

Pounds. 

Gallons. 

Cost  per 

Ton. 

Mt.  Morgan,  Queensland  

I 

•\T. 

3O 

80 

$7    ^O 

Haile  Mine,  S.  Carolina  

I 

ie 

IO 

I2O 

4.    6"? 

Oolden  Reward,  Dakota  

I 

40 

ir 

TOO 

ir  .  ro 

Gibbonsville  Idaho 

I 

12 

5OO 

Gillette  Colorado 

j 

•7  O—J.O 

I  ^—2O 

.uu 

North  Brookfield,  Nova  Scotia.  .  .  . 

I 

3° 

15 

Cost  if  to  2  cents 

per  pound. 

T.  K.  Rose  says  that,  "  at  ordinary  temperatures,  water  will 
absorb  2l/3  volumes  of  chlorine  gas  and  enough  lime  is  added  to 
have  the  solution  in  the  barrel  saturated." 

The  time  of  rotating  the  barrel  or  vessel  varies  from  two  to 
six  hours. 


256 


NOTES   ON  ASSAYING. 


The  following  series  of  tests  may  be  tried  to  see  if  a  satisfactory 
extraction  can  be  obtained: 


Percentage  of 

the  Roasted  Ore 

No. 

Weight  of  Ore 

H2O  Used. 

Taken. 

Treatment. 

Acid. 

Bleach. 

A 

300  gms. 

70%  of  ore 

i% 

1% 

Rotate  i£  to  3  hours. 

B 

2% 

i% 

C 

«        tt 

<t     tt  1  1 

2% 

i% 

j  Add  \  and  rotate  i  hour. 
j  Add  rest  and  rotate  i  hour. 

D 

it        tt 

tt     tt  it 

?% 

l*% 

Rotate  2  hours. 

E 

n       tt 

tt     ttit 

3% 

ll% 

j  Add  \  and  rotate  i  hour. 
|  Add  rest  and  rotate  i  hour. 

F 

it        it 

tt     tt  it 

4% 

2% 

Rotate  2  hours. 

G 

tt        tt 

It          It      1C 

4% 

2% 

«       3      tt 

H 

tt       it 

1  1       ft    tt 

5% 

2%% 

«            3           " 

•J 

The  smallest  percentage  of  chemicals  that  will  give  a  satis- 
factory extraction  having  been  determined,  the  next  experiments 
should  be  made  in  regard  to  the  time  necessary  to  give  an  equally 
good  extraction.  The  shorter  the  time,  the  greater  the  number 
of  charges  per  twenty-four  hours,  consequently  the  larger  the 
tonnage  per  day  and  the  smaller  the  cost  of  treatment  per  ton. 

These  data  having  been  established,  the  student  should  con- 
firm the  smaller  tests  by  making  tests  on  a  much  larger  scale. 


THE  CYANIDE  PROCESS  FOR  TREATMENT  OF  GOLD  ORES. 

Concentrates  from  stamp-mills  and  ores  high  in  sulphurets  and 
rich  in  gold  were  formerly  either  smelted  or  else  roasted  and  chlor- 
inated by  some  of  the  well-known  processes,  such  as  the  Plattner 
or  barrel.  The  cyanide  process  was  intended,  and  it  was  origi- 
nally claimed  for  the  process  that  it  would  treat  ores  of  this  char- 
acter, as  well  as  mill  tailings,  in  a  raw  condition,  a  large  per- 
centage of  the  gold  and  a  part  of  the  silver  going  into  solution  as 
cyanides.  Many  ores  can  be  treated  successfully  in  a  raw  con- 
dition, but  many  others  have  to  be  roasted  first.  They  are  next 
treated  with  an  alkali  wash,  if  necessary,  and  finally  with  weak 
solutions  of  KCN.  The  size  of  the  material  varies  from  f -mesh  to 
slimes,  but  the  coarser  the  ore  can  be  kept,  owing  to  the  ques- 
tion of  leaching,  with  a  satisfactory  extraction,  the  better. 


METALLURGICAL  LABORATORY  EXPERIMENTS.  257 

KCN  exposed  to  air  deliquesces  and  emits  HCN  as  well  as 
ammonia  : 


2KCNO  +4H2O  =  K2CO3  +  (NH4)2CO3; 
KCN  +  O    (air)   =KCNO. 

Cyanicides  are  substances  like  iron  or  copper  which  destroy 
KCN: 

Fe  +  6KCN  +  2H2O  =  K4FeCN6  +  2KOH  +  2H. 

The  KCN  solutions  vary  from  .005  to  -|%;  weak  solutions. 
apparently  have  a  greater  solvent  power  upon  gold  than  the 
stronger  ones.  Air  is  supposed  to  be  a  great  factor  in  the  solu- 
tion of  the  gold  : 


i.e.  2X196:4X65=3:2,  or  2  parts  KCN  should  dissolve  3  parts 
of  gold,  but  in  practice  30  to  50  parts  are  required.  The  follow- 
ing are  also  said  to  take  place: 


2Au+4KCN+H2O2         =  2KCN,2AuCN  +  2KOH. 

The  gold  may  be  precipitated  from  the  auric  cyanide  by- 
zinc  shavings,  by  zinc  dust,  by  charcoal,*  or  by  electrolysis. 
When  zinc  is  used  we  have  2KAuCN2+Zn  =  2Au  +  K2ZnCN4, 
i.e.,  i  Ib.  of  zinc  should  recover  6  Ibs.  of  gold,  but  in  practice 
it  only  recovers  about  i  ounce  of  gold. 

In  practice,  consumption  of  KCN  per  ton  of  ore  is  J  Ib.  to  i  J  Ibs. 
it       n  (i  (i  zjnc        ll    lt    li    <l    ll  ^  Ib  '  '     3  " 

FeSO4,  oxalic  acid,  H2S,  and  reagents  which  throw  down 
gold  from  AuCl3,  do  not  throw  it  down  from  the  auric  cyanide. 
In  the  present  tests  we  will  not  attempt  to  recover  the  gold  from 
the  2KAuCN2,  but  will  base  the  extraction  upon  the  assay  of 
the  ore  before  and  after  treatment  with  the  KCN.  In  testing 

*  See  Mining  and  Metallurgy,  vol.  7,  1898-99,  p.  190. 


258  NOTES   ON  ASSAYING. 

ores  by  this  process,  the  following  points  would  naturally  have 
to  be  decided : 

i st.  Is  the  ore  or  material  adapted  to  this  process;  free 
H2SO4,  FeSO4,  and  copper  salts  not  only  interfere  with  it,  but 
increase  the  consumption  of  the  cyanide : 

2KCN-f-H2SO4  =  K2SO4  +  2HCN  (hydrocyanic  acid); 
2KCN  +  FeSO4  =  K2SO4  +  FeCN2  (ferrous  cyanide) ; 
6KCN  +  FeSO4  =  K2SO4  +  K4FeCN4 

or  FeCy2 + 4KCN  =  K4FeCN6  ; 
FeC03  +  6KCN  =  K2CO3  +  K4FeCN6. 

2d.  How  coarse  can  the  ore  be  kept  while  yet  allowing  a 
successful  extraction  (fine  ores,  slimes,  and  especially  aluminous 
ores  are  difficult  to  leach  and  filter). 

3d.  What  percentage  of  KCN  will  extract  the  highest  per- 
centage of  gold  with  the  smallest  consumption  of  itself. 

4th.  The  proper  strength  of  KCN  having  been  found,  what 
is  the  shortest  length  of  time  the  ore  can  be  left  in  contact  with 
it,  still  giving  you  a  successful  extraction. 

5th.  Can  the  extraction  be  improved  either  by  agitating  the 
ore  and  the  solution  or  by  aerating  them. 

Tests  can  be  made  as  follows: 

Ore  treated  in  open  beakers. 

Ore  treated  in  closed  vessels. 

Ore  agitated  in  open  or  closed  vessels. 

Ore  acted  on  for  a  long  time,  solution  drawn  off,  and  then  treated 
with  a  weaker  solution. 

Ore  acted  on  during  several  periods,  either  short  or  long,  and 
allowed  to  aerate  between  them. 

Ore  kept  in  agitation  and  aerated  at  the  same  time. 

Experiment. — Sample  and  assay  the  original  ore.  Take  2  A.T. 
to  500  grammes  of  ore  (I  prefer  to  take  two  portions  of  2  A.T. 
each),  and  treat  for  a  given  length  of  time  with  a  solution  of  KCN, 
according  to  the  data  given  on  the  bulletin-board,  an  example  of 
which  is  given  on  page  261. 


METALLURGICAL  LABORATORY  EXPERIMENTS.  259 

Filter  by  decantation  on  a  large  filter  and  wash  thoroughly 
with  water.  The  nitrate  is  thrown  away.  Invert  the  filter  and 
contents  on  a  roasting-dish  and  heat  first  in  front  of  the  muffle, 
then  within,  and  finally  burn  the  filter.  Weigh 
the  residue,  and  if  it  is  caked  or  in  lumps,  pass 
it  through  a  sieve  slightly  coarser  than  the  one 
through  which  the  ore  was  originally  crushed. 
Mix  thoroughly  and  divide  the  ore  into  two 
equal  portions  by  placing  a  spatula  full,  first  on  one  balance-pan  of 
the  pulp- balance  and  then  on  the  other,  until  they  exactly  balance. 
Transfer  one  portion,  if  ore  is  as  fine  as  3o-mesh,  without  any 
further  grinding,  to  a  crucible,  and  then  weigh  the  other.  Make 
record  of  the  weight.  Assay  both  portions,  which  may  not  check 
exactly,  owing  to  the  coarseness  of  the  ore,  but  this  saves  grind- 
ing, and  as  we  obtain  the  total  gold  in  the  total  ore  it  is  immaterial 
whether  they  check  or  not. 

The  total  ore  after  treatment  could  be  assayed  in  one  crucible, 
but  if  the  crucible  was  eaten  through  or  any  accident  occurred, 
the  test  would  have  to  be  repeated;  therefore  the  tailings  are 
divided  into  two  equal  portions  and  assayed  separately. 

From  these  data  and  the  assay  of  the  original  ore,  calculate 
the  percentage  of  gold  extracted.  The  ore  to  be  tested,  the 
experiments  to  be  made,  and  the  data  to  be  obtained,  will  be  posted 
upon  the  bulletin-board. 

Report. — The  report  upon  this  process  should  be  handed  in 
with  the  following  data  and  table: 

Number  of  the  sample  or  name  of  the  ore. 

Character  of  the  ore. 

Size  of  the  ore,  i.e.,  what  sieve  it  will  pass  through  and  whether 
it  is  raw  or  roasted. 

Assay  of  the  ore. 

Amount  of  solution  and  the  percentage  of  KCN  in  the  solution 
used  upon  the  ore. 

Period  of  contact  of  this  solution  with  the  ore. 

Conditions  under  which  it  acted;  i.e.,  was  an  open  or  closed 
vessel  used;  were  the  ore  and  solution  agitated;  was  the  ore 
aerated  ? 


260 


NOTES  ON  ASSAYING. 


Diameter  of  vessel  used  and  depth  of  ore  and  solution  in  the 
vessel. 


Ore 

Used 
2  A.T. 

Total 
Gold  in 
Ore  Used, 
Gms. 

Weight  of 
Ore  after 
KCy 
Treat- 
ment. 
Gms. 

Assay  of 
Ore  after 
Treat- 
ment. 
Gms. 

Total 
Gold 
in  Tail- 
ings 
(a), 
Gms. 

Total  Gold  in 
Tailings  (&),* 
Gms. 

Extract- 
ed, 
Based 
on  (a). 

Extract- 
ed, 
Based 
on  (b). 

EXAMPLE 
No.  i. 

.00136 

28.915 

.  00008 

Assay 

2 

1.36  oz. 

.00272 

28.900 

.  00008 

.00016 

.000l6l 

94-i% 

94% 

EXAMPLE 

No.  2. 

.03820 

27.140 

.0007 

27.140 

.0007 

.00140 

.00150 

96.33% 

96.07%: 

The  KCy  solution  from  the  last  test  was  evaporated  down  with  PbO   (30 
grammes)  and  the  residue  fused  in  a  glazed  crucible. 
Gold=. 03640  grammes,  or  an  extraction  of  95.28?^. 

Treatment  of  Ores  by  Potassium  Cyanide. — In  testing  a  raw 
ore  to  see  whether  it  is  amenable  to  this  treatment,  I  prefer  to 
use  fine  ore — that  is,  ore  passing  a  30-  or  4O-mesh  sieve  at  least — 
and  treat  it  with  a  strong  solution — that  is,  \%  to  J%  solution— for 
a  long  period  of  time,  196  hours  or  more.  This  will  give  some 
idea  of  its  amenability.  If  the  results  are  negative  then  make 
the  same  tests  on  some  ore  which  has  been  roasted.  If  these  give 
negative  results,  then  some  modification  of  the  process,  such  as 
aeration,  agitation,  or  percolation,  will  have  to  be  tried. 

If  the  tests  on  the  raw  ore  (through  30-  or  4o-mesh)  give 
satisfactory  results,  then  of  course  roasting  is  unnecessary,  but  it  is. 
necessary  to  determine  the  best  strength  of  KCN,  how  coarse  it 
is  possible  to  keep  the  ore  and  the  shortest  and  best  method  of 
contact.  To  do  this,  take  the  same  ore,  keep  time  of  treat- 

*  There  is  probably  a  mechanical  loss  of  tailings,  and  these  tailings,  which  in 
Example  No.  I  amount  to  half  a  gramme,  are  assumed  to  assay  the  same  as  those 
saved- 


METALLURGICAL   LABORATORY  EXPERIMENTS. 


261 


merit  the  .same  (196 'hours),  and  decrease  tlie  percentage  of  KCN 
in  the  solution  until  the  extraction  begins  to  decrease.  Having 
determined  the  weakest  solution  that  can  be  used  to  advantage, 
keep  the  time  of  contact  the  same  and  experiment  with  coarser 
ore  until  size  limit  of  ore  is  reached. 

Next  make  tests  and  see  whether  it  is  not  possible  to  shorten 
time  of  contact  by  means  of  a  series  of  alternate  contacts  and 
Derations  or  by  aeration  alone.  Agitation  may  also  be  tried  and 
experiments  carried  on  in  regard  to  bromo-cyanogen.  In  the 
treatment  of  some  ores  the  first  KCN  solution  is  a  strong  one 
followed  by  a  weaker  one;  in  other  ores  the  treatment  is  just 
the  reverse. 

When  the  small  tests  give  satisfactory  results  they  should  be 
confirmed  by  tests  on  a  larger  scale  and  the  consumption  of 
KCN  carefully  determined.  This  last  is  especially  important, 
ior,  owing  to  the  poor  quality  of  air  in  laboratories,  tests  made 
there  usually  show  a  much  higher  consumption  than  those  made 
in  a  mill  or  in  places  where  the  surrounding  air  is  purer. 


EXPERIMENTAL  TESTS  ON  A  GOLD  ORE  AS  TO  ITS  ADAPTABILITY 
FOR  THE  CYANIDE  PROCESS. 

Silicious  ore  carrying  i£  per  cent  FeS2.     Raw,  crushed  through  2o-mesh  sieve. 
Assay,  .38.  oz.     Value  @  $2ofl7/ioo  per  oz.  =  Sy85/^,,. 


No.  of  Tests 

Weight 
of  Ore 
Taken. 

Water 
Used. 

Per  Cent 
ofKCy 
in  Solu- 
tion. 

Time  of 
Contact, 
Hours. 

Extrac- 
tion, 
Per 
Cent. 

A 
B 
C 

2  A.T. 

60  c.c. 

1 

16 
16 

48 

65 
66$ 

82 

(Washed  with  water  and  then 
with    a    weak    solution    of 
KOH  and  again  with  water, 
before  treatment  with  KCy. 

D 

'« 

it 

48 

59 

Did  not  wash. 

E 

tt 

1 

48 

76$ 

"     "       " 

P 

It 

" 

I2O 

96 

Roasted     the     ore     and     then 

washed  with  KOH  and  H2O. 

" 

I2O 

89 

Raw  ore;    did  not  wash. 

140 

94 

H            (I           <  (           f  I                 « 

1 

ft 

(4 

9° 

95 

Treated  in  an  inverted  bottle. 

262  NOTES  ON  ASSAYING. 

In  the  last  test  the  ore  is  first  kept  in  contact  with  the  KCN 
solution,  then  allowed  to  aerate  (time  of  contact 
40  hours,  time  of  aeration  10  hours) ,  again  placed 
in  contact,  and  then  washed  with  water. 
The  above  tests,  with  the  exception  of  I, 

-Filter  plate 


were  made  in  open  beakers,  and  the  ore  was 

< — Glass  tube 

O-  ^-ciamp  n°t  stirred   or   agitated.     They   indicate    that 

this  ore  can  be  treated  successfully  by  this 
process,  that  a  J%  solution  of  KCN  seems  better  than  J%, 
and  that  roasting  and  aerating  both  increase  the  extraction. 
Further  tests  should  be  made  in  regard  to  the  time  of  contact,  and 
tests  on  large  amounts  of  ore  should  be  made  to  see  whether  they 
confirm  the  small  ones,  and  also  in  regard  to  the  consumption  of 
KCN. 


THE   CYANIDE   PROCESS    AS   APPLIED   TO   THE    CONCENTRATES 
FROM   A  NOVA  SCOTIA   GOLD    ORE  * 

THE  following  work,  performed  by  Mr.  W.  A.  Tucker,  of  the 
class  of  1893,  in  the  Mining  Department  of  the  Massachusetts 
Institute  of  Technology,  seems  to  me  to  be  worthy  of  publication. 
I  believe  it  has  always  been  considered  that  the  presence  of  arsenic 
especially  interferes  with  the  extraction  of  gold  by  the  cyanide 
method.  Mr.  Tucker's  work,  although  made  on  a  laboratory 
scale,  certainly  seems  to  disprove  this  view,  and  to  show  that, 
even  with  a  very  large  percentage  of  arsenic  present  in  the  ore, 
a  high  extraction  may  be  obtained  without  an  excessive  con- 
sumption of  KCN. 

The  ore  from  which  the  concentrates  were  obtained  was  a 
gray  argillaceous  schist  and  slate,  with  stringers  and  veins  of 
quartz  running  through  it.  It  carried  free  gold  and  about  12  per 
cent  of  sulphides.  The  ore  was  crushed  with  stamps;  the  free 
gold  was  collected  in  the  ordinary  way  on  silver- amalgamated 
copper  plates;  and  the  sulphides,  which  consisted  chiefly  of 

*  Transactions  of  the  American  Institute  of  Mining  Engineers.  Florida  Meet- 
ing, March,  1895 


METALLURGICAL  LABORATORY  EXPERIMENTS.  263 

arsenopyrite  and  pyrite,  with  very  small  amounts  of  galena  and 
chalcopyrite,  were  concentrated  and  collected  by  means  of  a 
Frue  vanner. 

A  carefully  taken  sample  gave: 

Gold 6.17  ounces  per  ton 

Arsenic 30 . 6    per  cent 

The  latter  figure  would  correspond  to  about  66.5  per  cent  of 
arsenopyrite  in  the  concentrates. 

The  work  to  be  done  was  outlined  as  follows: 

1.  Sizing  the  concentrates; 

2.  Assaying  the  different  sizings; 

3.  Treating   these    different    sizings   with  KCN  of   different 
degrees  of  strength  for  different  periods  of  time. 

Owing  partly  to  the  small  amount  of  concentrates  found  on  the 
40-  and  6o-mesh  sieves,  and  partly  to  the  lack  of  time,  the  follow- 
ing four  series  were  substituted  in  place  of  carrying  out  No.  3: 

Series  I. — Treating  concentrates  with  a  given  amount  of  a 
i  per  cent  KCN  solution  for  different  periods  of  time.  The  solu- 
tion, instead  of  being  all  added  at  once,  was  added  in  three  portions. 

Series  II. — Treating  a  given  amount  of  concentrates  with  an 
equal  quantity  of  a  i  per  cent  solution  of  KCN  for  different 
periods  of  time,  the  KCN  not  being  renewed  as  in  Series  I. 

Series  III. — The  same  as  Series  II,  except  that  the  con- 
centrates were  revolved  with  the  KCN  solution  in  bottles,  and 
did  not  simply  stand  in  contact  with  it,  as  in  the  previous  series. 

Series  IV. — Concentrates  and  solution  in  motion;  strength 
of  KCN  solution,  time  of  contact  and  amount  of  solution  varying. 

SIZING   AND   ASSAYING   CONCENTRATES. 

A  sample  of  the  concentrates  sized  and  assayed  resulted  as 
follows : 


264 


NOTES  ON  ASSAYING. 


Sieve 

Mesh. 

Proportion  of 
Sample. 

Assay. 
(Ounces 

Gold. 

Proportion  of 
Total  Gold. 

Through. 

On. 

(Per  Cent.) 

per  Ton.) 

(Per  Cent.) 

4O 

0.412 

2^  .  7O 

0.000363 

1  .  71 

40 
60 
80 

60 

80 

0.449 
4.010 
02    7IO 

27.  10 
10.69 
6  oo 

0.000417 
0.001468 

O    OIOOO^ 

1.96 
6.90 
80    4.3 

Lost 

2    4.IQ 

Total 

IOO    OOO 

O.O2I2CC3 

IOO   OO 

The  above  assays  include,  of  course,  the  free  gold  (pellets) 
which  may  have  been  found  on  the  40-,  60-,  and  8o-mesh  sieves. 

TREATMENT  WITH   CYANIDE. 

Series  I. — One  A.T.,  or  29.166  grammes,  of  concentrates 
passed  through  a  3o-mesh  sieve,  and  assaying  6.17  ounces  per 
ton,  was  treated  with  100  c.c.  of  KCN  (i  per  cent)  solution.  This 
-solution  was  added  at  three  different  times  in  equal  portions, 
the  first  portion  being  drawn  off  before  the  second  was  added, 
and  so  on. 

The  apparatus  employed  was  an  inverted  glass  bottle,  with 
the  bottom  cut  off,  and  a  perforated  porcelain  plate  laid  across 
•at  the  point  of  contraction  to  the  neck,  so  as  to  form  (in  the  in- 
verted position)  a  false  bottom.  Below  this,  the  neck  was  closed 
with  a  rubber  stopper,  through  which  passed  a  glass  tube,  fitting 
outside  to  a  rubber  tube,  closed  with  a  pinch-cock. 

The  result  of  these  tests  was  as  follows: 


Time 

of  Adding  KCN  , 

Time  of 

Calculated  from  First" 
Addition. 

Withdraw- 
ing the  Third 
Addition  of 
KCN. 

Assay  of 
Tailings  in 
Ounces  per 

Percentage 
of  Gold 
Extracted. 

Grammes  of 
KCN 
Consumed. 

Grammes  ot 
KCN  Used 
per  Gramme 
of  Gold 

Second. 

Third. 

Ton. 

Extracted 

(Hours.) 

(Hours.) 

(Hours.) 

16^ 

20* 

23 

1.92 

68.88 

O.II2 

26.4 

1  6 

20* 

23 

2-39 

61.26 

0.124 

32-8 

23^ 

3° 

51 

1-43 

76.82 

0.168 

35-4 

22 

29* 

51 

2.82 

54-29 

o.  146 

43-6 

23 

65 

70 

1.44 

76.66 

0-155 

32-8 

23 

65 

70 

2.78 

54-94 

0.156 

46.0 

24 

44 

94 

i-5i 

75-52 

o.  169 

36.3 

24 

44 

94 

2.67 

56.72 

0.206 

58-9 

24 

44 

94 

I-51 

75-52 

o.  165 

35:4 

H 

20^ 

1 

94* 
94* 

118 
118 

1.62 
1.56 

73-74 
74.72 

o.  164 

0.202 

36.0 
43-8 

20* 

94* 

1x8 

1.23 

80.06 

0.202 

40.9 

METALLURGICAL   LABORATORY  EXPERIMENTS. 


265 


These  results  were  not  at  all  satisfactory,  for  they  neither  indi- 
cated that  the  extraction  increased  with  the  time  of  contact,  nor 
did  they  show  in  what  period  of  the  contact  the  solution  of  the 
gold  took  place. 

Series  II. — The  apparatus  used  was  the  same  as  in  Series  L. 
Quantity  of  concentrates  (through  3o-mesh),  25  grammes;  assay, 
6.17  ounces  per  ton;  quantity  of  KCN  (i  per  cent)  solution,  25  c.c. 
The  solution  was  not  changed. 

These  experiments  seem  to  show  that  the  extraction  of  gold 
increases  with  the  time  of  contact  of  the  KCN.  Apparently,  the 
consumption  of  KCN  increases  with  the  time.  This  large  con- 
sumption in  both  Series  I  and  II  is  no  doubt  due  to  the  free 
access  of  air  to  the  apparatus  in  which  the  tests  were  made. 

While  working  on  these  experiments,  25  grammes  of  concen- 
trates and  25  c.c.  of  KCN  solution  were  put  in  a  bottle,  tightly 
stoppered,  which  was  caused  to  revolve.  The  extraction  was 
such  an  improvement  on  all  the  previous  work  that  all  other 
experiments  (Series  III  and  IV)  were  conducted  in  this  way. 


Duration 
of  Treatment. 
(Hours.) 

Assay  of  Tailings. 
(Ounces  per 
Ton.) 

Per  Cent,  of 
Gold  Extracted. 

Grammes  of 
KCN  Consumed. 

Grammes  KCN 
Used  per  Gramme 
of  Gold  Extracted. 

16 

2.97 

51.84 

.064 

23-4 

16 

2-75 

55-43 

.065 

22.2 

22 

2.30 

62.72 

.058 

J7-5 

22 

2.17 

64.83 

.058 

16.9 

25i 

2.12 

65.64 

.065 

19.6 

71 

2.51 

59-32 

.124 

39-5 

7i 

2.24 

63.69 

.Il8 

35-0       . 

7i 

2-57 

58-35 

.127 

41.1 

118 

1.61 

73-91 

.091 

23-3 

118 

1.40 

77-31 

•  i3x 

32.5 

118 

1.26 

79.58 

.134 

31-1 

Series  III. — Quantity  of  concentrates  (through  30- mesh),  25 
grammes;  assay,  6.17  ounces  per  ton;  quantity  of  KCN  (i  per 
cent)  solution,  25  c.c.  Bottles  and  contents  revolved. 


266 


NOTES  ON  ASSAYING. 


Duration  of 
Revolution. 
(Hours.) 

Assay  of  Tailings. 
(Ounces  per 
Ton.) 

Per  Cent  Ex- 
tracted.Calculated 
from  No.  2. 

Grammes  of 
KCN  Consumed. 

Grammes  of  KCN 
Used  per  Gramme 
of  Gold  Extracted. 

2 

0-39 

93.68 

0.022 

4-44 

2 

I.  II 

82.01 

0-033 

7.6o 

2 

0.82 

86.71 

0.035 

7-63 

2 

0.82 

86.  7I 

0.032 

6.97 

4 

0.66 

89.30 

0.072 

I5-25 

4 

0.62 

89.95 

0.042 

8.82 

5* 

0.58 

90.60 

0.053 

1  1.  06 

Si 

0.47 

92.38 

0.063 

I3-07 

23 

0.42 

93-19 

0.031 

6.42 

23 

0.58 

90.60 

0.043 

8.98 

Tnese  experiments  seem  to  indicate  that  to  revolve  the  bottles 
about  six  hours  was  sufficient,  and  that  the  extra  amount  of  gold 
extracted  would  hardly  compensate  for  a  longer  revolution. 

Series  IV. — Bottles  and  contents  revolved. 

The  large  consumption  of  KCN  in  the  last  two  tests  was  due 
to  insufficient  washing. 

In  none  of  the  tests  were  the  concentrates  washed  with  water 
previous  to  their  treatment  with  cyanide.  Owing  to  lack  of  time, 
Mr.  Tucker  was  unable  to  test  the  solutions  for  arsenic,  or  to 

CONCENTRATES  THROUGH  30-MESH;    ASSAY,  6.17  OUNCES  PER  TON. 


Duration 
of  Revo- 
lution. 
(Hours.) 

Weight 
of  Ore. 
(Grms.) 

Strength 
of  KCN. 
(Per 
Cent.) 

Quantity 
of  KCN 
Solution. 
(c.c.) 

Assay  of 
Tailings. 
(Oz.  per 
Ton.) 

Per  Cent 
of  Gold 
Extracted. 

Grammes 
of  KCN 
Consumed. 

Grammes 
of  KCN  per 
Gramme  of 
Gold  Ex- 
tracted. 

4 

50 

I.O 

25 

0.87 

85.90 

.026 

2.84 

4 

5° 

I.O 

25 

0.71 

88.49 

.094 

10.03 

4 

25 

o-5 

25 

0.47 

92.38 

.014 

2.86 

4 

25 

o-5 

25 

0.66 

89.30 

.009 

1.91 

4 

25 

o-5 

25 

0.89 

85.57     - 

.014 

3-09 

i64 

25 

o-5 

25 

°-97 

84.28 

•055 

12.33 

i<3 

25 

o-5 

25 

0-57 

90.76 

.050 

10.42 

23 

25 

0-5 

25 

0.51 

91-73 

•045 

9.28 

CONCENTRATES  THROUGH  SO-MESH;    ASSAY,  6  OUNCES  PER  TON. 


Duration 
of  Revolu- 
tion. 
(Hours.) 

Weight 
of  Ore. 
(Grms.) 

Strength 
of  KCN. 
(Per 
Cent.) 

Quantity 
of  KCN 
Solution. 
(c.c.) 

Assay  of 
Tailings. 
(Oz.  per 
Ton.) 

Per  Cent 
of  Gold 
Extracted. 

Grammes 
of  KCN 
Consumed. 

Grammes 
of  KCN  pec 
Gramme 
of  Gold 
Extracted. 

6f 

IOOO 

I.O 

IOOO 

0.70 

88.30 

7-033 

77.06 

6* 

IOOO 

0-5 

IOOO 

I.  00 

83-33 

3.617 

4O.  22 

METALLURGICAL  LABORATORY  EXPERIMENTS.  267 

see  whether  all  the  gold  could  be  recovered  from  them;  so  we 
are  unable  to  give  any  data  on  these  points.  While  we  realize 
that  these  are  simply  laboratory  experiments,  that  the  tailings 
are  in  all  cases  too  rich  to  be  thrown  away,  still  we  consider  the 
extraction  remarkably  high  on  material  carrying  the  percentage 
of  arsenic  that  this  does.  Making  the  tests  in  a  closed  vessel 
lessens  the  consumption  of  KCy,  as  one  would  expect.  As  the 
extraction  also  increases,  this  would  seem  to  be  contrary  to 
Eisner's  equation,  to  which  oxygen  is  necessary;  and  certainly 
there  could  hardly  be  enough  in  a  small  bottle  to  influence  the 
extraction.  Keeping  the  ore  and  solution  in  agitation  certainly 
seems  to  have  helped  the  extraction,  although  this  method  of 
working  has  met  with  very  little  success  in  actual  practice. 

REACTIONS   IN  THE   CYANIDE   PROCESS. 

The  following  are  some  of  the  simpler  reactions  which  take 
place  in  various  stages  of  the  process: 

In  Preliminary  Treatment. 


Fe2O3,2SO3  +  4NaOH+  H2O  =  Fe2H6O6+ 
FeSO4  +  CaH2O2  =  FeH2O2+  CaSO4. 
ZnSO4+  2NaOH  =  ZnH2O2+  Na2SO4. 

In  Solution  Tanks. 

4KCy+  2Au+  H2O+  O  =  2KAuCy2+  2KOH. 
4KCy-f  2Ag+  H20+  O  =  2KCy,2AgCy  +  2KOH. 
sKCy+  FeSO4  =  FeCy2+  K2SO4. 


Fe2(S04)3  +  6KCy  +  6H2O  =  Fe2H6O6+  3K2SO4+  6HCy. 
3K2ZnCy4+  4Au+  2<3  =  4KAuCy2  +  K2ZnO2+  2ZnCy2. 
A12(S04)3+  3H20  +  6KCy  =  A12O3+  s^SO,  +  6HCy. 

In  Air. 

2KCy+  CO2+  H2O  =  2HCy+  K2CO3. 
KCy-f  O  =  KCyO.     2KCNO  +  30  =  K2CO3+  CO2+  2N 
2KCy+  2H2O  =  2HCy+  2KOH. 


268  NOTES  ON  ASSAYING. 

Substances  in  Solution. 

=  K2O,ZnO+  2KCy+  2H2O. 


K2ZnCy4  +  CaH2O2  =  ZnH2O2  +  2KCy+  CaCy2. 

In  Precipitating-tanks  and  Zinc  Boxes. 
2KAuCy2+  Zn  =  K2ZnCy4+ 


ZnH202+  2KCy  =  ZnCy2+  2KOH 
Zn+Cy2  =  ZnCy2 
ZnCy2+  2KCy  =  K2ZnCy4 
2KOH+C02  =  K2C03+H20 
HCy+KOH  =  KCy+H20 
Electrolysis  will  give  from  KAuCy2=Au+K+2Cy: 


2KOH+  Zn  =  ZnK2O2+  2H. 

Testing  a  Roasted  Ore  for  Sulphates.  —  The  following  test  will 
determine  if  a  natural  ore  or  one  that  has  been  roasted  contains 
salts,  soluble  in  water,  which  would  be  detrimental  to  the  Cyanide 
Process  : 

Take  100  to  300  grammes  of  the  ore  and  put  in  some  vessel, 
add  300  c.c.  of  water,  stir  for  5  minutes  or  so  and  filter.  Add 
slowly  a  small  amount  of  KCy  solution  of  the  same  strength  to 
be  used  in  leaching  the  ore.  Watch  the  solution  carefully  for  any 
cloudiness.  If  none  appears  the  ore  is  ready  to  be  treated  or  is 
probably  dead  roasted.  If  a  brown  color  shows,  soluble  salts 
of  iron  are  present  in  the  ore  ind  will  cause  a  high  consumption  of 
KCy  and  precipitation  of  ferrocyanide  compounds  in  the  zinc- 
boxes  : 

FeSO4+2KCy=K2SO4+FeCy2  (ferrous  cyanide). 

If  a  blue  coloration  occurs,  followed  by  a  blue  or  greenish 
precipitate,  then  the  ore  contains  a  large  amount  of  sulphates 
and  a  very  high  consumption  of  KCy  will  take  place: 

FeCy2  +  4KCy  =  K4FeCy6   (potassium  ferrocyanide)  . 

Alkali  or  Alkali  Wash.  —  Many  ores  are  quite  acid,  especially 
those  that  have  been  much  weathered.  This  acidity  is  generally 


METALLURGICAL  LABORATORY  EXPERIMENTS.  269 

due  to  the  presence  of  sulphates,  especially  FeSO4.  To  determine 
the  amount  of  lime  or  alkali  to  add  to  an  ore  in  order  to  neutralize 
this  acidity  proceed  as  follows: 

Dissolve  10  grammes  of  NaOH  in  1000  c.c.  of  water.  /.  each 
cubic  centimeter  contains  .01  grammes  of  NaOH. 

Take  200  grammes  of  ore  and  leach  thoroughly  with  water. 
Titrate  this  solution  with  NaOH. 

If  we  run  in  26.2  c.c.  of  NaOH  solution,  then  it  takes  .262 
grammes  of  NaOH  to  neutralize  the  acidity  of  200  grammes  of 
ore  or  2.62  Ibs.  to  neutralize  2000  Ibs.  of  ore. 

Poisoning.  —  Potassium  cyanide  is  a  deadly  poison  and  very 
quick  in  its  action;  therefore  when  large  amounts  of  solution  con- 
taining KCy  are  being  discharged  from  mills,  the  matter  is  a 
serious  one.  Hydrocyanic  acid  acts  directly  on  the  nervous 
system,  causing  instant  paralysis  (jaws  close  and  it  is  necessary 
to  use  force  in  opening  them);  hence  any  treatment  that  will 
excite  the  action  of  the  nerves,  such  as  the  application  of  cold 
water  to  the  spine  and  inhalation  of  ammonia,  may  be  tried  in 
cases  of  faintness  produced  by  breathing  the  vapor  of  the  acid. 
When  KCy  gets  into  cuts  it  may  produce  painful  sores,  and  men 
employed  in  melting  the  zinc  slimes  are  subject  to  an  eruption  on 
the  arms  and  often  complain  of  headache  and  giddiness.  Ferro- 
cyanide  of  potash  has  been  recommended  for  the  eruption.  For 
cases  of  internal  poisoning  freshly  precipitated  carbonate  of  iron 
given  immediately  is  a  good  antidote  (FeCO3  +  6KCy  =  K4FeCye 
+  K2CO3),  potassium  ferrocyanide  being  formed  in  the  stomach. 
Next  give  a  purgative.  Walk  person  about  and  prevent  sleep. 

The  FeCO3  is  obtained  by  ado!  ng  a  solution  of  carbonate  of 
soda  to  ferrous  sulphate  (FeSO4  +  Na2CO3  =  FeCO3  +  Na2SO4), 
and  a  bottle  of  each  of  these  should  be  kept  constantly  on  hand 
in  every  place  where  KCy  is  being  used.  The  freshly  precipi- 
tated white  carbonate  of  iron  should  be  given  immediately,  for  it 
soon  oxidizes  to  the  brownish  -black  ferrous  hydrate,  and  this  to 
the  ferric  hydrate: 

FeCO3+H2O 


2FeH2O2  +  H2O  +O  =  Fe2H6O8. 


Dr.  C.  J.    Martin  and  Mr.  R.  A.  O'Brien,  Proceedings  of 


NOTES  ON  ASSAYING. 


'Society  of  Chem.  Industry  of  Victoria,  Vol.  I,  pp.  119-129,  have 
'experimented  on  rabbits  with  many  antidotes.  They  recom- 
mend ferrous  sulphate  and  potash  together  with  powdered  mag- 
nesium oxide,  which  must  be  given  as  soon  as  possible  and  within 
5  minutes  of  the  time  of  taking  the  cyanide.  They  advise  keep- 
ing on  hand: 

1.  30  c.c.  (i  oz.)  of  a  23  per  cent  solution  of  ferrous  sulphate. 

2.  30  c.c.  (i  oz.)  "  "  5   "     "         "       "  caustic  potash. 

3.  2  grammes  (30  grains)  powdered  magnesia. 

4.  A  vessel  to  mix  them  in. 

5.  Stomach-pump. 

Nos.  i  and  2  should  be  kept  in  hermetically  sealed  tubes 
which  can  be  easily  broken.  Break,  pour  contents  in  the  vessel, 
^add  the  magnesia,  a  pint  of  water,  shake  well,  and  administer.'* 

Some  cases  of  poisoning  occurring  when  men  are  treating  the 
zinc-box  residues  have  been  found  to  be  due  to  arsenic  and  not 
to  KCN. 

If  an  ore  contains  arsenic,  some  of  this  metal  will  be  deposited 
on  the  zinc.     When  the  zinc  is  treated  with  acid  later  on,  the 
deadly  arseniuretted  hydrogen  will  be  given  off: 
Zn3As2+  3H2SO4  =  2AsH 


or 


Potassium  Cyanide.  —  Practically  pure  KCN  can  be  purchased, 
which  should  be  used  to  standardize  the  silver  nitrate  solutions. 

The  ordinary  commercial  KCN  is  far  from  pure,  as  will  be 
seen  from  the  following  analyses: 


No.  i. 

No.  2. 

No.  3. 

No.  4. 

No.  5. 

T'otassiuni 

?8   *% 

C4    2% 

18% 

21  89< 

Sodium        

jo  4 

none 

2Q    3 

27    I 

CN       .             

38.2 

18.2 

14  4 

TOO 

n  69< 

(^  f\    /Calculated   froms 
-v's  v       carbonates       ) 
Caustic  alkali.  . 

I.O 

3-2 

12.2 

2-3 

8.7 

7-9 

21.4 
1.8 

Cl         

none 

none 

14.  2 

8.3 

CNO 

none 

ii   6 

none 

none 

In  KCN  there  is  40%  CN;  therefore  the  per  cent  purity  of 
the  above  lots  would  be 
38.2  18.2 

40  4° 


-4Si%,     36%,     47i%,     34%- 


METALLURGICAL   LABORATORY  EXPERIMENTS.  271 

Titration  of  the  KCy  Solution.  —  Take  an  aliquot  part  of  the 
KCy  solution,  add  a  few  drops  of  a  5%  solution  of  KI  as  an 
indicator  and  run  in  from  a  burette  a  standard  solution  of  neutral 
AgNO3.  The  end-point  is  a  pale  bluish  coloration  with  a  slight 
precipitate  of  AgCy.  Double  cyanides  of  metals  and  potassium 
do  not  interfere  with  the  titration.  Silver  cyanide  is  insoluble 
in  water,  but  is  soluble  in  KCy  and  CaCy2;  therefore,  while 
these  are  present,  the  AgCy  thrown  down  is  immediately  dis- 
•solved;  when  they  are  neutralized,  the  AgCy  will  remain  as  a 
precipitate. 

Any  KCyO  present  in  the  solution  will  also  give  a  precipitate 
until  neutralized. 

The  reactions  which  take  place  are  as  follows: 

10.  KCy  +AgNO3  =  AgCy  +KNO3. 

ib.  AgCy  +  KCy  =  KAgCy2. 

2.  KAgCy2+AgNO3  =  KNO3-J-2AgCy  (end-point:    white  pre- 
cipitate). 

3.  AgNO3+KI    (indicator)  =  KNO3+AgI  when   no  KCy   is 
present. 

If  in  equation  (2)  we  continue  to  add  AgNO3,  after  the  white 
precipitate  first  appears,  a  precipitate  will  continue  to  come 
down  until  all  the  KAgCy2  in  the  solution  is  broken  up. 

If  too  much  alkali  has  been  used  as  a  wash,  we  may 
obtain  CaCy2  in  this  way:  K2ZnCy4+CaH2O2=  ZnH2O2+ 
2KCy+CaCy2. 

From  the  reaction  AgNO3+2KCy  =  KAgCy2+KNO3  we  see 
that  i  part  AgNO3  is  equivalent  to  2  parts  KCy,  or  170  parts 
AgNO3  can  be  added  to  130.2  parts  KCy  before  a  precipitate 
comes  down. 

or    1.3056  AgNO3. 


If,  therefore,  we  add  1.3056  grammes  AgNO3  to  a  litre  of 
water,  it  will  correspond  to  i  gramme  KCy,  and  each  c.c.  will 
contain  .001305  grammes  of  AgNO3  and  correspond  to  .001 
^grammes  KCy. 

Suppose  that  50  c.c.  of  some  unknown  KCy  solution  takes 


272 


NOTES  ON  ASSAYING. 


50  c.c.  or  .06525  AgNO3  to  neutralize  it,  then  we  know  that  this 


corresponds  to  .050  KCy,  or  the  solution  contains  L      =  .i%KCy. 

5° 

TREATMENT     OF     ROASTED     GOLD     ORES     BY     MEANS     OF 

BROMINE* 

Mr.  H.  R.  Batcheller,  of  the  class  of  1894,  Massachusetts  Insti- 
tute of  Technology,  while  experimenting  with  chlorine  gas  on  a  cer- 
tain lot  of  roasted  concentrates,  met  with  the  following  difficulties  : 
i.  A  poor  extraction  of  the  gold.  2.  A  very  large  consumption  of 
chlorine  gas.  3.  Inability  to  precipitate  all  of  the  gold  from  the  solu- 
tion containing  the  AuCl3.  4.  The  bullion  obtained  was  very  base. 

These  difficulties  were  the  same  whether  the  chlorine  was 
generated  from  H2SO4,  MnO2,  and  salt,  or  whether  H2SO4  and 
bleaching-powder  were  used.  They  may  be  accounted  for  partly 
by  the  presence  of  some  arsenic  left  in  the  roasted  ore,  and  partly 
by  the  presence  of  copper  in  the  solution  containing  the  AuCl3. 

It  was  therefore  suggested  to  try  the  effect  of  bromine  on  a 
similar  lot  of  ore.  The  use  of  this  element  is,  of  course,  nothing 
new,  but  in  the  following  experiments  it  seemed  to  present  many 
advantages  over  chlorine. 

The  material  worked  upon  consisted  of  some  concentrates 
containing  2.31  ounces  of  gold  per  ton  and  34.26  per  cent  of 
arsenic,  which  would  correspond  to  about  74.4  per  cent  of  arseno- 
pyrite.  Considerable  pyrite  and  a  small  amount  of  galena  and 
chalcopyrite  were  also  present. 

The  material  when  sized  and  assayed  showed: 


Per  Cent. 

Ounces  Gold  per 
Ton. 

On  24-mesh  sieve  

•7 
1.9 

3-5 
6.0 

4-5 
II.  O 

26.0 

45  -° 
1.4 

j-  Assaying  1.4 

\  Assaying  1.2 

Assaying  1.  12 
Assaying  i  .  19 
Assaying  1.4 

On  3o-mesh  sieve  

On  4o-mesh  sieve  

On  ^o-mesh  sieve 

On  6o-mesh  sieve 

On  8o-rnesh  sieve   .  .  . 

On  loo-mesh  sieve      ...            .... 

Through  loo-mesh  sieve  

Loss  

100.00 

*  Transactions    of    the  American    Institute    of    Mining    Engineers. 
Meeting,  March,  1895. 


Florida 


METALLURGICAL  LABORATORY  EXPERIMENTS. 


273 


The  line  of  treatment  was  as  follows: 

1.  Roasting  the  concentrates  in  a  reverberatory  furnace. 

2.  Submitting  the  roasted  ore  to  bromination  in  strong  pre- 
serve-jars, "  Lightning  "  brand,  with  double  gaskets,  the  jars  and 
their  contents  being  revolved  during  the  experiment. 

3.  Precipitation  of  the  gold  by  means  of  H2S: 

ROAST  I. — Time,  five  hours. 


Kilos. 

Assay, 
Ounces  Gold. 

IO 

2.31 

6 

3.36 

Per  Cent. 
40 

Per  Cent. 
12.7 

BROMINATION. 

Roasted  ore 500  grammes 

Bromine 14  •  5  c.c. 

Water 500  c.c. 

Time si  hours 

Assay  of  tailings  from  two  tests  gave  0.30  and  0.32  ounces  of 
gold.  Based  on  the  roasted  ore,  this  would  be  an  extraction  of 
90.7  per  cent. 

ROAST  II. — Time,  eight  hours. 


Kilos. 

Assay, 
Ounces  Gold. 

Itj 

2    •?! 

Roasted,  ore     ..      

4..  20 

Per  Cent. 
46.67 

Per  Cent. 

I 

The  following  experiments  were  made  to  determine  the  proper 
amount  of  bromine  for  500  grammes  of  ore: 


Roasted  Ore, 
Grammes. 

Bromine,  c.c. 

Time,  Hours. 

Water,  c.c. 

Extraction,  based  on 
Assay  of  Tailings, 
i^er  Cent. 

CQO 

30 

cl 

C.QO 

QO    67 

COO 

3O 

11 

C.OO 

80    27 

CQO 

I    c 

3 

C.OO 

O2    C4. 

C.QO 

I  .O 

si 

C.OO 

81   « 

CQO  .  . 

o.  e. 

11 

C.OO 

62    2  3 

CQO.  .                    

o.  3 

Si 

C.OO 

f.         6 

60.  oo 

274 


NOTES   ON  ASSAYING. 


The  following  were  made  to  determine  the  shortest  period  of 
contact  of  ore  and  bromine  giving  a  good  extraction: 


Roasted  Ore, 
Grammes. 

Bromine,  c.c. 

Time,  Hours. 

Water,  c.c. 

Extraction,  based  on 
Tailings,  Per  Cent. 

<OO    . 

I  .  cr 

rri 

t?OO 

02    ^4. 

1OO.  . 

I  .  e 

4* 

sOO 

88  oo 

C.OO.  . 

I  .  e 

7i 

c;oo 

86  oo 

•CQO 

I    c 

2 

coo 

81   3^ 

C.OO.  . 

I  .  c 

I 

ZOO 

72.02 

These  tests  seem  to  indicate  that  1.5  c.c.  of  bromine,  added  to 
500  grammes  of  ore  in  500  c.c.  of  water,  would  effect  in  five  and 
one  half  hours  an  extraction  of  over  90  per  cent  of  the  gold  in 
the  ore. 

To  test  these  conclusions,  a  third  roast  was  made: 

ROAST  III. — Time,  eight  hours.     (Ore  cooled  in  furnace.) 


Kilos. 

Assay, 
Ounces. 

Arsenic, 
Per  Cent. 

Sulphur, 
Per  Cent. 

Raw  ore  

70 

2  .  31 

34   26 

Roasted  ore  

43.  7 

«.«8 

O.  II 

O    34 

Loss 

Per  Cent. 
^7-6 

Per  Cent. 
•}    ? 

oo  67 

Of  this  roasted  ore,  15  kilos  were  treated  with  45  c.c.  of 
bromine  in  15  kilos  of  water  for  four  and  one  half  hours  in  a 
revolving  keg.  The  tailings  showed  an  extraction  of  85.5  per 
cent. 

As  an  excess  of  bromine  was  present  when  the  keg  was  opened, 
at  the  end  of  four  and  one  half  hours,  a  second  experiment  was 
tried  with  ore,  15  kilos;  bromine,  35  c.c.;  time,  five  and  one  half 
hours;  water,  15  kilos. 

This  showed  an  extraction  of  92.18  per  cent,  based  on  the 
assay  of  the  tailings.  The  actual  gold  recovered  from  the  solu- 
tion was  only  about  80  per  cent,  which  may  be  accounted  for 
by  the  presence  of  considerable  copper  in  the  solution. 

The  expulsion  of  the  bromine  from  the  solution  seemed  to  be 
best  brought  about  by  means  of  SO2.  Air  and  steam  were  both 
tried,  but  with  poor  success.  After  the  passage  of  SO2  the  solu- 


METALLURGICAL  LABORATORY  EXPERIMENTS.  275 

tion  was  quite  clear,  although  some  gold  would  be  precipitated 
on  standing. 

When  the  ore  was  chlorinated  the  solution  at  this  point,  con- 
taining the  AuCl3,  would  be  quite  turbid,  and  evidently  con- 
tained a  large  amount  of  base  metals  as  chlorides.  These  would 
necessarily  interfere  with  the  complete  precipitation  of  the  gold, 
besides  making  the  bullion  base.  Some  base  metals,  such  as 
copper,  were  also  present  in  the  bromine  solution,  but  apparently 
not  to  such  an  extent,  for  the  solution  was  clear. 

The  gold  was  finally  precipitated  by  means  of  H2S. 

In  the  experiments  on  this  particular  ore  bromine  seemed  to 
have  the  following  advantages  over  chlorine: 

1.  It  extracted  a  much  higher  percentage  than  chlorine,  the 
results  being  estimated  not  only  on  the  assay  of  the  tailings,  but 
also  on  the  actual  gold  recovered. 

2.  It  gave  solutions  much  more  free  from  base  metals.     This 
would  be  expected,   especially  where   chlorine  is  generated   by 
means  of  H2SO4  and  bleaching- powder,  and  the  acid  has  a  chance 
to  act  directly  on  the  ore. 

3.  Less  time  is  required  to  extract  the  gold. 

4.  The  ease  in  using  and  comfort  in  handling  is  much  greater. 
As  regards  the  comparative  cost,  the  least  amount  of  bromine 

which  could  be  used  on  this  ore  with  a  successful  extraction 
appeared  to  be  0.3  per  cent,  or  6  pounds  per  ton.  With  bro 
mine  at  25  to  40  cents  per  pound,  this  would  make  the  cost  very 
high;  but  the  cost  of  chlorination  would  certainly  be  still  higher, 
as  it  was  found  necessary  to  use  as  high  as  10  per  cent  of  lime 
and  6  per  cent  of  H2SO4  to  obtain  even  a  fair  extraction. 

Cyanogen  Bromide. — This  salt,  discovered  by  Serullas  in  1827, 
is  supposed  to  have  a  greater  solvent  action  on  gold  than  cyanide 
alone.  Serullas  prepared  it  as  follows: 

One  part  of  bromine  is  poured  upon  two  parts  of  cyanide  of 
mercury  contained  in  a  tubulated  retort  or  glass  tube  closed  at 
the  bottom  and  surrounded  with  ice;  bromide  of  mercury  and 
bromide  of  cyanogen  are  formed  with  great  evolution  of  heat. 

The  bromide  of  cyanogen  sublimes  in  needles  contaminated 
at  first  with  bromine,  but  ultimately  the  bromine  flows  back  and 


,  276  NOTES  ON  ASSAYING. 

enters  completely  into  combination.  Gentle  heat  is  then  applied 
and  CNBr  sublimed  into  a  receiver  connected  with  the  retort 
and  surrounded  with  ice. 

Roscoe  and  Schorlemeyer  say  cyanogen  bromide  is  formed  by 
the  action  of  bromine  on  hydrocyanic  acid  or  on  metallic  cyanides. 

If  bromine  is  added  drop  by  drop  to  a  well-cooled  aqueous 
solution  of  potassium  cyanide,  crystals  separate  out  which  con- 
sist of  a  mixture  of  cyanogen  bromide  and  potassium  bromide. 
When  these  crystals  are  heated  to  a  temperature  of  from  60°  to 
65°,  cyanogen  bromide  sublimes  in  the  form  of  delicate  trans- 
parent prisms,  which  soon  pass  into  the  cubical  form. 

The  salt  is  poisonous  and  acts  powerfully  on  the  eyes, 

EXPERIMENTAL  TREATMENT   OF   GOLD-BEARING    ORES  * 

The  following  questions  often  come  up  and  require  answer- 
ing in  regard  to  samples  from  prospect-holes,  as  well  as  regards 
the  ore  from  mines  in  actual  operation. 

1 .  What  value  has  the  ore  ? 

2.  Is  it  a  free-milling  ore? 

3.  If  so,  what  percentage  of  the  gold  can  be  extracted  by 
amalgamation  or  by  passing  the  ore  over  amalgamated  or  silver 
amalgamated  copper  plates?    (All  gold  which  is  free  will  not 
necessarily  amalgamate.) 

4.  What  value  have  the  tailings  after  this  treatment  ? 

5.  What  percentage  of  concentrates  does  the  original  ore  carry? 

6.  What  value  have  these  concentrates;    that  is,  will  it  pay 
to  put  in  some  kind  of  concentrating  machinery  in  order  to  save 
the  concentrates,  or  can  the  tailings  from  the  plates  be  treated 
directly  with  KCN? 

These  questions  can  of  course  be  answered  in  the  most  satis- 
factory manner  by  having  from  15  to  20  or  more  tons  crushed 
and  tested  in  some  gold-mill,  provided  with  all  the  modern 
appliances  for  crushing,  amalgamating,  and  concentrating. 

They  can,  however,  be  very  well  answered  by  means  of  the 
following  tests: 

*  See  Canadian  Mining  Review,  October  31,  1898. 


METALLURGICAL  LABORATORY  EXPERIMENTS.  277 

Test  jor  No.  I. — Weigh  the  ore.  Crush  down  gradually  and 
then  sample  very  carefully.  Sample  should  be  weighed  before 
passing  it  through  each  sieve,  and  especial  care  should  be 
observed  in  regard  to  any  residue  left  on  any  sieve  or  any 
pellets  of  gold  found  on  said  sieve.  These  should  be  carefully 
saved  and  assayed  separately.  The  final  sample  for  assay  should 
be  crushed  through  a  i2o-mesh  sieve  at  least.  (Assay  notes, 
Sampling  Ores.)  Assay.  If  pellets  have  been  found,  calculate 
them  in  the  final  result.  Give  the  ounces  the  ore  runs  per  ton 
of  2000  Ibs.  and  the  value  per  ton. 

Tests  for  Nos.  2,  3,  and  4  can  best  be  made  by  treating  the 
ore  by  one  of  the  following  methods: 

The  ore  should  pass  a  3o-mesh  sieve  at  least. 

a.  In  a  miner's  ordinary  gold- pan.     Take  300  to  500  grammes 
of  ore,  which  has  previously  been  carefully  sampled  and  assayed. 
Mix   into  a  thick   pulp   with  35   to  60%    of   water   (depending 
upon   the    character  of   the  ore),   and  then    add   5    to   10%    of 
clean  mercury.     Shake  up  well  for  some  time  and  pan  down  in 
the  usual  manner.      Separate  the  mercury  and    amalgam  from 
the    ore    and   concentrates.      Save   all    the   water,    concentrates, 
tailings,  and  slimes.     Filter  the  whole,  or  else  allow  them  to  settle 
overnight,  decant  off  water,  dry,  weigh,  and  assay  the    tailings. 
The  sample  for  assay  should  be  crushed  through  a  1 2o-mesh  sieve. 
Calculate  from  this  assay  the  total  gold  in  the  total  tailings,  then 
calculate  the  total  gold  in  ore  taken  for  amalgamation.     The  dif- 
ference is  the  gold  amalgamated.     Figure  the  percentage.     The 
mercury  and  amalgam  may  be  retorted,  or  if  small  in  amount, 
treated  with  dilute  nitric  acid  in  a  parting-flask. 

In  this  parting  heat  the  solution,  but  do  not  allow  the  action 
to  become  very  violent.  The  gold,  unless  at  the  very  end  the 
amalgam  is  touched,  will  be  left  in  beautiful,  fine,  yellow,  needle- 
like  crystals.  Wash  free  from  acid  and  the  nitrates  of  mercury, 
transfer  to  an  annealing-cup,  heat  in  a  muffle,  and  weigh. 

b.  In  a  good  stout  bottle  or  fruit-jar.     Take  200  grammes  to 
one  kilogramme  of  ore,  place  in  jar,  add  5  to  10%  of  mercury,  and 
sufficient  water  to  make  the  whole  into  a  thick  pulp.      Stopper  the 
jar  tightly  and  shake  up  and    down  vertically  for  one  half-hour 


278  NOTES  ON  ASSAYING. 

or  else  revolve  three  hours.     Pan  down  as  usual  and  treat  the; 
tailings  and  mercury  as  described  under  method  a. 

c.  Crush  the  ore  through  30-  or  4o-mesh  screen  and  pass  it 
over  silver- amalgamated  copper  plates.     Plates  are  then  scrape:! 
and    freed    from  the  silver-gold    amalgam,   which    is    retorted. 
(See   Retorting   Mercury.) 

The  tailings  are  collected,  dried,  weighed,  and  assayed. 

Sample  for  assay  should  be  crushed  through  i2o-mesh  sieve. 

This  method  may  not  give  quite  as  high  an  extraction  as 
when  the  ore  is  stamped  and  then  goes  over  the  plates,  because 
the  grinding  and  polishing  action  of  the  stamps  on  the  gold  is, 
lacking. 

d.  In  the  Ball  Mill.      (See  page  279.) 

Test  for  No.  5. — Take  from  500  to  2000  grammes  of  the  ore,, 
after  amalgamation,  through  40- mesh  sieve  (an  ore  through  30-  or 
4o-mesh  sieve  is  sufficiently  fine  for  all  these  tests;  otherwise  the 
concentrates  will  be  slimed),  and  carefully  pan  or  van  it  down,  or 
else  pass  it  through  a  hydraulic  classifier.  (See  page  280.) 

Dry  and  weigh  the  heads,  and  be  sure  not  to  have  the  heat  so- 
great  as  to  roast  the  sulphides  and  thus  alter  their  weight. 

Test  for  No.  6. — Assay  the  concentrates  obtained  in  No.  5  by 
crushing  them  all  or  a  sample  of  them  through  a  i2o-mesh  sieve. 

A  true  value  of  the  tailings  from  the  above  tests  can  only  be 
obtained  by  saving  all  the  water  and  ore  and  slimes.  Owing 
to  the  difficulty  of  obtaining  check  assays  on  an  ore  carrying  free 
gold,  the  true  value  should  be  based  on  the  total  amount  of  gold 
recovered  by  amalgamation  plus  the  total  gold  found  in  the  con- 
centrates and  tailings  afterwards. 

Example  oj  Treatment. — Sample  received  weighed  20  kilo- 
grammes; it  was  crushed,  sampled,  and  assayed  to  obtain  the 
value  in  gold  per  ton. 

500  grammes  of  the  ore  were  taken  and  the  concentrates 
removed  by  panning,  to  determine  the  percentage  per  ton  of  2000 
Ibs. ;  also  to  find  how  many  tons  would  concentrate  into  one. 

15  kilogrammes  were  amalgamated  and  the  mercury  and 
amalgam  retorted.  Both  the  concentrates  and  tailings  were 
saved,  weighed,  and  valued. 


METALLURGICAL   LABORATORY  EXPERIMENTS. 


279 


We  then  had: 


Ig  and  amalgam, 
which  was  retorted. 


Concentrates. 
Weighed,  sampled, 
and  assayed. 


Tailings. 

Weighed,  sampled, 
and  assayed. 


The  report  read  as  follows: 

The  ore  assayed  4  oz.  gold  per  ton  of  2000  Ibs.  @  $2o67/100  per  oz.=      ,$82.68 
500  grammes  ore,  through  3o-mesh,  gave  20  grammes  concentrates 

=  4  per  cent  in  ton  of  ore. 
15  kilos,  of  ore  were  amalgamated;   gold  contents  as  per  assay 2 .0565  gms. 

The  amalgam  (retort  residue)  gave 1.7452  gms.  gold  =        84.86% 

Concentrates,  600  grammes  after  amalga- 
mation (assay  14.58  oz.  per  ton) 3000  "  "  =  14.58 

Tailings,  14350  grammes  (assay  .02  oz.  per 

ton) 00976  "  "  .47 

Loss  in  tailings  (50  grammes)  by  difference.     .00150     "       "  =  .07 


2.05646  99.98% 

If  ore  contains  4  per  cent  of  concentrates,  25  tons  will  concentrate  into  one,  for 
80  :  i  : :  2000  :  x. 

FREE-MILLING   TEST  IN   BALL  MILL. 

First  clean  out  the  mill  thoroughly,  which  can  be  done  with 
a  stiff  brush,  some  water  and  sand,  to  remove  anything  left  from 


Opening 


; 

• 

fcfi        ' 

1          9 
b 

o  £     ' 

' 

« 

I          0 

IP, 

1 

1 

3_ 

« 

1 

_n 

1 

i 

3 

Cylinder  for 

y   i 

i 

| 

j    y 

a 

7, 

/, 

previous  test.     Be  very  sure  to  get  no  oil  or  grease  inside  of  the 
mill,  otherwise  the  mercury  will  " sicken"  or  "flour"  badly. 

Weigh  out  2  to  5  kilogrammes  of  ore  for  each  side  and  charge 
it  at  opening  (b)  on  the  side,  the  plug  (a)  having  previously  been 
screwed  in  tight.  Add  35  to  60%  of  water,  to  make  the  pulp 
into  a  thick  mud,  and  then  add  i  to  5  iron  balls.  If  the  ore  is 
rich  in  sulphurets  or  arsenical  compounds,  use  only  one  or  two 


280 


NOTES  ON  ASSAYING. 


balls.  These  will  keep  the  ore  well  stirred  up  and  will  be  less 
liable  to  make  slimes  and  flour  the  mercury.  Stop  up  opening  (b) 
and  start  mill  in  order  to  grind  the  ore.  If  ore  is  through  30- 
mesh  sieve,  amalgamate  directly,  for  grinding  is  unnecessary,  and 
i  or  2  balls  will  be  sufficient.  After  the  ore  is  sufficiently  fine, 
amalgamate  by  one  of  the  following  methods: 

a.  With  200  gm.  of  mercury  alone. 

b.  "     «*     «      «       «          andiogm.  KCN. 

c.  "     "     "      "     •"          and  50  ' '  sodium  amalgam .* 

d.  "     "     "      "       "          and  50  "  mercuric  chloride, 

and  then  later  on  add  10  "  KCN. 

Methods  b  and  c  simply  clean  off  the  oxides  and  other  com- 
pounds soluble  in  these  substances,  and  they  keep  the  Hg  bright 


Callings) 


Hydraulic     k_ J 
water 


Amalgam, 
Hg.  and 

Concentrates!;^ 

Classifier. 

and  active.      In  d  the  corrosive  sublimate  (HgCl2)  brings  about 
electric  action  between  the  gold  particles  and  the  iron,  the  iron 

*  About  97%  Hg  and  3%  Na. 


METALLURGICAL  LABORATORY  EXPERIMENTS.  281 

being  the  poles  and  the  HgCl2  the  electrolyte.    Amalgamate  in 
all  the  methods  from  J  to  3  hours. 

To  clean  up  test,  take  out  cap  (&),  add  some  water  and  dis- 
charge contents  through  the  opening  (a)  into  iron  kettles  or 
wooden  pails.  Finally  clean  out  inside  of  mill  with  a  stiff  brush. 
Save  all  water,  sand,  and  slimes. 

The  mercury  and  amalgam  may  be  separated  from  the  sand 
by  means  of  a  gold-pan,  a  vanning-shovel,  or  by  a  hydraulic  classifier. 

This  last  is  the  quickest,  but  not  necessarily  the  most  satisfactory. 

If  the  vanning-shovel  is  used,  do  not  put  too  much  material 
upon  it  at  one  time. 

Shake  and  settle  the  mercury  very 
thoroughly  upon  the  van  before  washing 
off  the  first  lot  of  waste.  Gradually 
bring  forward  the  concentration  until  it 
consists  largely  of  mercury  and  concen- 
trates. Then  pour  the  Hg  into  a  bowl 
and  save  the  concentrates. 

Repeat  the  vanning  upon  another  por- 
tion of  the  pulp,  and  so  on  until  all  is  treated.     Finally  pan  all 
the  concentrates  once  more  for  any  drops  of  Hg,  and  then  clean 
the  mercury  for  retorting. 

If  the  Hg  from  any  of  the  tests  is  found  to  be  "  foul "  or 
"  leady  "  or  in  a  "  floured  "  condition,  it  is  well  not  to  separate 
it  too  cleanly  from  the  pyrite  and  other  concentrates;  but  to 
carry  some  of  these  along  with  it.  Now  cover  the  mercury  and 
concentrates  with  a  little  water  and  try  to  clean  and  collect 
the  mercury  by  adding  either  a  small  piece  of  KCN,  a  little  ammo- 
nia, or  some  KOH.  If  these  fail  to  clean  and  bring  it  together, 
wash  thoroughly  with  water,  leaving  the  mercury  just  moist, 
and  add,  one  at  a  time,  a  few  small  slivers  of  metallic  sodium, 
Ttfhich  will  always  bring  all  the  mercury  together. 

Save  all  the  sand,  slimes,  and  water.  Filter  them  or  allow 
them  to  settle  overnight  or  until  the  water  is  clear,  then  decant  or 
siphon  off  the  water,  dry  residue,  weigh;  pass  through  sieve  fine 
enough  to  remove  all  lumps,  sample  and  assay.  Grind  the  sample 
for  assay  through  i2o-mesh  sieve. 


282  NOTES  ON  ASSAYING. 

This  method  is  better  than  taking  a  running  sample  from 
the  classifier,  because  it  is  sure  to  save  all  the  slimes,  which  are 
very  often  the  richest  portion  of  the  tailings  and  which  would 
otherwise  be  lost. 

The  mercury  and  amalgam  are  cleaned  and  retorted  and  the 
residue  treated  as  per  ''Retorting  Mercury,"  page  290. 

Report  the  following  data: 

Character  and  composition  of  the  ore  as  ascertained  by  inspec- 
tion and  panning. 

Size  of  ore  as  received  and  treated. 

Method  employed  in  amalgamation  test  and  chemicals  used, 
if  any. 

Time  taken  in  grinding  the  ore. 

Time  taken  in  amalgamation. 

Condition  of  the  mercury  at  the  end  of  the  test,  i.e.,  whether 
it  was  bright  and  clean  or  dull  and  foul. 

If  the  ore  contains  both  gold  and  silver,  hand  in  a  report 
upon  each  separately. 

x= weight  of  original  ore.     Assay.  Total  gold  =  a. 

y  =  tailings  (after  panning  off  Hg) .   Assay.    Total  gold  =  6. 
a-b  =  gold  amalgamated  =  - . 

c 

-  =  percentage  of  gold  amalgamated. 

Tailings  (y)  are  panned  or  freed  from  concentrates.  We 
then  have  concentrates  (M)  and  tailings  (AT). 

Weigh  and  assay  M.     Weight  of  gold  in  M  =  d. 

Weigh  and  assay  AT.     Weight  of  gold  in  N  =  e. 

The  weight  of  y  should  equal  M-\-N.    y—M  should  equal  AT. 

The  gold  in  c,  d,  and  e  should  equal  that  in  a.  We  shall  then 
have 

—  percentage  of  gold  amalgamated. 

of  gold  saved  in  heads  and  concentrates. 

—  of  gold  lost  in  final  tailings. 

—  of  gold  unaccounted  for. 

100 

Mercury  used         =  200  grammes. 

"        recovered  =-i  97         "         =98.5%. 


METALLURGICAL  LABORATORY  EXPERIMENTS. 


283 


For  further  data  as  to  reporting  results  see  page  279,  "Experi- 
mental Treatment  of  Gold-bearing  Ores." 

AMALGAMATION    OF   GOLD    ORES. 

Stamp-mill  Work. — The  two  following  runs  give  an  idea 
of  the  work  which  the  small  stamp-mill  in  this  laboratory 
will  do: 

The  mill  has  three  stamps  weighing  225  Ibs.  each,  made  up 
as  follows : 

Rod 35 . 3  kilos 

Boss 27.9     " 

Shoe 22        " 

Tappet 17.4     " 

The  dies  weigh  10.4  kilos  each. 

The  shoes  and  the  wooden  wedges,  with  which  they  are  fastened! 
on  to  the  boss,  have  the  following  dimensions : 


Wedge 


Dia 


The  tailings  from  the  plates  were  concentrated  on  a  full-size 

4-foot  Frue  vanner. 

ORE  No.  1490. 

Two  portions  of  a  Nova  Scotia  gold  ore 
divided  while  in  a  coarse  condition. 

A      (2i"t03"°    B 
Assay i .  25  oz.  i .  17  oz. 

Total  ore  crushed,  kilos 343i  339 .  & 

Rate  per  24  hours  (3  stamps),  tons 1.6  i .  62 

Sieve  (punched)  corresponding  to 4o-mesh         30  (steel  wire)1 

Drop  of  stamps,  inches 5!  5 J 

No.  of  drops  per  minute 97  98 

Feed-water  per  24  hours,  gallons 5108  — 

Slope  of  plates,  inches  per  foot if  i .  37 

Concentrates  in  ore,  per  cent 3-^7  S«S3 

Concentrates,  ounces  per  ton .58  .74 

Vanner  tailings  (314  kilos),  ounces .02  .53 

Ore  lost  during  process,  per  cent 7*85  7.7 

Mercury  was  used  in  the  battery  in  both  runs. 


284 


NOTES  ON  ASSAYING. 


GOLD   ACCOUNT. 

Total  gold  in  ore,  based  on  assay,  gms . .     14.69110 

Saved  in  battery,  grammes. . . 

"      on       "  '     plate, 
"      "   plate  i,  copper,         " 
*'      "      (t      2,  Muntz  metal,*  gm. . 
*'      "      "      3,  copper,  grammes. .. 

i  t         (i         ie         .  (t  « 

•<(  t   (  C   t  -  ((  « 

•"      "      "      6,  Muntz  metal,  gm. . . 
"      "      "      7,  copper,  grammes. .. 


Mercury  trap 
*  60%  Cu,  40%  Zn. 


13.53062-98.43% 

Length  of  plates,  75  inches. 

Area  of  outside  amalgamating  surface,   1587     sq.  in. 
"     "  inside  "  "  83}    "  " 

Silver  amalgam  was  spread  over  the  plates  with  a  brush,  and  was  scraped  off 

after  the  run  and  retorted. 

Gold  actually  extracted,  based  on  assay. . .   78. 16%  91 

Per  cent  of  the  gold  saved,  which  was  col- 
lected in  the  battery  (^f^j)   98. 18  97.83 

SIZING    OF   THE   BATTERY  TAILINGS. 


"      60 

"      80 

Through 


14.69110                13.63113 

.   io.93520                    12.10840 

.33854                        .11872 

.08087  " 

r   .06604 

.03011 

"8 

bO 

1    .04287 

.03385 

C 

jg  .04162 

.02105 

rt   £ 

£  .02629 

.01050 

.       V)    <U 

'     «  tn     ' 

^•01254 

.00468 

ex  .01666 

.oo6n 

1 

£  .01038 

.00878 

T  .01038 

.        .00736  . 

I  .00682 

.00470                         .03720 

11.48175                     12.49792 
In  tailings  c6c? 

In  concentra 

tes.    . 

.  .    .4675 

Per  Cent. 

Per  Cent 

808 

On  30  sieve 

.  OO  ' 

. 

60  sieve 

3 

,  <jy«j 

•93 

Thro.  30  on 

40  sieve. 

.08' 

[Too  little 
f  to  assay. 

80     " 

5- 

,02  J 

"       40   " 

50     " 

.38 

' 

IOO       " 

5 

•51  r95'°3 

"       50  " 

60     " 

I 

.51 

.  12   OZ. 

IOO       " 

84 

•So* 

"       60  " 

So     " 

3 

•3i 

.06  oz. 

"      80  '/ 

IOO       " 

9 

.28 

.06  oz. 

99 

,86 

Through 

IOO       " 

»S 

•44 

.  14  oz. 

Making  Silver  Amalgam. — Unless  the  amount  of  acid  and 
mercury  is  in  the  right  proportion  to  the  silver  taken,  the  amal- 
gam will  not  come  out  satisfactorily  and  a  basic  nitrate  of  mer- 
cury or  a  blue  powder  will  be  liable  to  form. 

Mr.  C.  I.  Auer,  class  of  1901,  took  this  subject  (the  making 
and  composition  of  silver  and  gold  amalgams)  as  a  thesis.  He 


METALLURGICAL   LABORATORY  EXPERIMENTS.  285 

found  that  the  following  rules  should  be  followed  in  making 
silver  amalgams: 

Have  the  silver  finely  granulated. 

Use  4  c.c.  of  HNO3  (sp.  gr.  1.20)  for  every  gramme  of 
silver. 

Cover  the  vessel  in  which  the  solution  takes  place,  and  heat 
gently,  but  do  not  boil,  that  the  silver  may  go  into  solution  quietly 
and  the  acid  not  evaporate.  Filter  off  the  gold,  if  any  is  present, 
add  8.6  c.c.  of  water  for  every  gramme  of  silver  taken,  and 
then  add  the  mercury  all  at  once.  Use  16  grammes  of  mercury 
for  every  gramme  of  silver. 

The  nitrate  of  silver  solution,  when  the  mercury  is  added, 
can  either  be  hot  or  cold. 

After  adding  the  mercury,  stir  the  solution  constantly  until 
all  the  silver  has  amalgamated.  If  a  silky  precipitate  comes 
down,  or  a  blue  powder  tends  to  form  and  grow  like  a  mush- 
room on  the  amalgam,  it  indicates  that  the  solution  is  not  suffi- 
ciently acid.  This  blue  powder  consists  of  Ag  and  Hg  in  vary- 
ing proportions.  Decant  the  nitrate  of  mercury  from  the  amal- 
gam into  a  wide-mouthed  bottle  and  wash  the  amalgam  once, 
by  decantation,  adding  this  washing  to  the  first  decantation.  Give 
the  amalgam  six  or  more  additional  washings,  stirring  it  thor- 
oughly with  a  large  porcelain  spatula.  Save  all  these  wash- 
ings in  another  bottle  separate  fubm  the  first  two  decantations. 
The  amalgam  is  next  squeezed  through  chamois  or  cotton  cloth 
and  the  excess  of  mercury  removed. 

Amalgam  made  as  above  may  be  strained  or  squeezed  through 
chamois,  linen,  canvas,  or  cloth.  After  being  squeezed  through 
these  by  hand  pressure,  the  residue  in  the  chamois  or  other  mate- 
rial will  carry  from  14.5  to  17.5  per  cent  of  silver,  depending 
upon  the  pressure,  the  material  used,  and  the  temperature  of 
the  amalgam  at  the  time  of  squeezing.  The  mercury  which 
passes  through  the  material  carries  about  .045  per  cent  of 
silver. 

When  the  amalgam,  squeezed  by  hand,  is  put  under  a  pres- 
sure of.  48,000  Ibs.  per  square  inch,  more  mercury  is  removed 
and  the  residue  contains  from  23  to  24.5  per  cent  of  silver. 


236  NOTES  ON  ASSAYING. 

The  mercury  removed  in  this  manner  carries  from  .05  to 
.06  per  cent  of  silver.  The  sp.  gr.  of  the  amalgam  containing  23 
to  24.5  per  cent  of  silver  is  13.7  to  13.76. 

Gold  amalgams,  when  squeezed  by  hand,  carry  from  32  to 
41  per  cent  of  gold,  and  the  mercury  removed  will  carry  from 
,12  to  .16  per  cent  of  gold.  When  placed  under  48,000  Ibs. 
pressure  the  percentage  of  gold  increases  to  44  or  48  per  cent. 
This  is  not  so  high  as  some  samples  of  scale  removed  from  plates 
that  have  been  given  to  me. 

One  sample,  taken  from  an  outside  plate  of  a  stamp-mill, 
carried  39.39  per  cent  of  gold  on  one  side  and  42  per  cent  on 
the  other. 

A  sample  of  very  hard  scale,  near  the  head  of  outside  plate 
•(six  months'  run),  carried  56.87  and  57.75  per  cent  of  gold. 

Recovery  of  Silver  and  Mercury  from  the  Nitrate  Solution. — 
Either  of  the  following  methods  can  be  used: 

1.  Put  in  iron  rods  or  scrap.     Both  Ag  and  Hg  will  be  thrown 
xlown,  after  some  time.     Clean  the  iron,  filter  solution,  and  retort 
the  residue. 

The  solution  must  not  be  too  acid,  because  a  great  deal  of 
iron  oxide  will  be  found  in  the  residue. 

2.  Throw  down  both  the  Ag  and  Hg  as  chlorides.     Filter, 
wash,  and  dry  them. 

Weigh  and  mix  with  one  fourth  their  weight  of  oxide  of  lime 
^CaO),  rubbing  them  together  in  a  mortar. 

Retort  this  mixture.  The  mercury  distils,  leaving  a  residue, 
containing  silver,  which  is  fused  with  a  little  soda,  silica,  and  a 
large  amount  of  borax  glass.  Cool  the  crucible,  break  it  and 
weigh  the  silver  button. 

BULLION. 

Melting  and  Refining. — The  following  notes  are  from  books, 
<iata  collected  at  smelting  works,  and  my  own  experience: 

A  good  furnace  with  a  splendid  natural  draft  or  with  air  sup- 
plied by  a  blower  is  the  first  requisite. 

If  large  graphite  crucibles,  i.e.,  Nos.  100  or  125  are  to  be  used, 


METALLURGICAL  LABORATORY  EXPERIMENTS.  287 

the  furnace  should  be  about  3'  6"  deep,  2'  6"  wide  at  bottom 
(inside),  and  2'  2"  at  the  top. 

The  flue  should  be  about  10"  below  top  of  furnace  and  8" 
by  12". 

The  black-lead  crucibles,  when  new,  should  always  be  heated 
slowly  while  upside  down;  when  red  they  should  be  turned  and 
placed  right  side  up.  They  should  stand  upon  a  3"  fire-brick 
placed  across  the  grate-bars.  The  tongs  with  which  to  handle 
these  crucibles  should  always  fit  well  about  them,  and  the  graspers 


(a),  in  figure  of  crucible,  should  come  well  below  the  bulge  or 
largest  part  of  the  crucible.  When  the  tongs  are  in  place,  slip  a 
ring  over  the  handles  to  hold  them  firm. 

Always  put  a  handful  of  borax  glass  into  crucible  before 
charging  the  bullion.  If  the  precious  metals  are  in  a  fine  con- 
dition, charge  with  a  scoop  or  a  funnel.  (See  cuts.) 

Gold,  precipitated  upon  zinc  in  the  KCN  process  or  from  an 
AuCl3  solution,  is  generally  mixed  thoroughly  with  from  one  and 
one-half  to  twice  its  weight  of  borax  glass  by  revolving  them  to- 
gether in  a  barrel  with  iron  balls.  The  mixture  is  then  charged 
directly  into  the  crucible.  Cover  crucible  and  heat  until  con- 
tents are  thoroughly  liquid. 

If  bullion  is  base,  nitre  and  borax  glass  are  both  needed  in 
refining,  but  too  much  nitre  will  rapidly  eat  into  the  graphite 
crucible.  Lead,  when  present  in  the  bullion,  is  best  oxidized  by 
nitre  or  sal-ammoniac;  tin  by  means  of  K2CO3;  Sb  and  As  by 
means  of  nitre  or  by  stirring  the  bullion  with  an  iron  rod. 
Iron  rust  can  be  removed  by  adding  CaSO4;  the  sulphur  taken 
up  by  the  metal  is  then  removed  by  stirring  the  bullion  with  an 
iron  rod.  Na2CO3  is  to  b  2  avoided  unless  there  is  silicious  mat- 
ter present;  still  a  little  of  it  with  nitre  seems  to  work  well  even 
if  bullion  is  quite  pure. 


288  NOTES  ON  ASSAYING. 

Bone-ash  and  sil'ca  save  the  crucible  from  the  action  of  the 
oxides,  and  are  especially  useful  for  thickening  the  slag  in  case 
skimming  is  necessary.     The  skimming  is  done  by  means 
of  an  iron  rod  coiled  as  in  the  adjoining  figure,  and  the 
spiral  then  bent  so  that  it  will  be  parallel  with  the  surface 
of  the  bullion  to  be  skimmed.     If  bullion  is  poured  to- 
gether with  the  slag — and  many  say  this  is  the  only  way 
to   obtain    a   clean  brick — the  slag  should  be  perfectly 
^      liquid. 

Toughening. — This  process  serves  to  eliminate  small  quantities 
of  impurities  like  As,  Pb,  Sb,  etc.,  which  would  render  the  bullion 
brittle  and  unfit  for  coinage  purposes. 

T.  K.  Rose  and  others  recommend  the  addition  of  a  little 
sal-ammoniac  or  corrosive  sublimate  to  the  melted  bullion. 

Cover  quickly  to  keep  volatile  chloride  fumes  out  of  the 
room.  Test  by  dipping  out  a  small  sample  and  casting  it  into- 
a  thin  ingot.  Cool  it  in  water  and  see  if  it  will  bend  upon 
itself. 

Pure  gold  is  a  brilliant  green  color  when  it  is  melted,  and  it 
may  then  be  poured. 

Silver,  when  nearly  pure,  often  bubbles  violently  in  the  crucible,, 
and  some  say  this  is  especially  so  when  much  nitre  has  been 
used  in  refining.  The  remedy  seems  to  be  to  lower  the  tempera- 
ture, cover  it  with  charcoal  and  stir  it  with  a  graphite  rod  until 
the  bubbling  ceases.  Then  pour. 

Pouring  and  Casting. — Always  stir  the  bullion  thoroughly 
before  doing  this,  and  if  a  sample  is  to  be  taken  for  assay,  take 
it  immediately  after  the  stirring.  Ingot  moulds  should  be  per- 
fectly bright  and  clean  and  heated  on  the  top  of  the  furnace 
until  they  are  too  hot  to  be  handled  with  the  bare  hands.  Some 
heat  them  almost  to  the  ignition-point  of  oil. 

As  regards  the  use  of  oil,  while  some  put  in  almost  J"  in  the 
large  moulds,  others  are  accustomed  to  use  only  a  little  around 
the  top  of  the  mould  and  none  at  the  bottom.  Fine  rosin,  sprinkled 
into  the  bottom  of  the  mould  just  before  pouring,  is  also  used. 

.The  object  of  the  oil  is  to  make  a  smoother  ingot  and  by  its 
burning  on  top  of  the  ingot  to  stop  all  sprouting  and  tarnish- 


METALLURGICAL   LABORATORY  EXPERIMENTS.  289. 

In  the  case  of  small  ingots  fine  charcoal  sprinkled  on  top,  as,, 
soon  as  the  pour  is  made,  will  also  answer  nicely.  Pour  the 
metal  quickly  and  carefully,  always  moving  the  crucible  back  and 
forth  over  the  mould  to  avoid  pouring  in  one  spot.  Pouring  in  one 
place  makes  a  poor  ingot  and  one  that  is  liable  to  stick  in  the  mould. 

Ingots  may  be  taken  out  when  they  are  still  hot,  and  if  not 
quite  clean  they  may  be  plunged  into  dilute  H2SO4. 

Too  much  care  and  attention  cannot  be  given  to  the  saving 
of  all  slags,  droppings,  and  skimmings.  The  floor  or  bench 
on  which  the  work  is  done  should  have  been  made  with  this 
especial  end  in  view,  and  should  be  perfectly  smooth  and  tight, 
that  the  slags,  etc.,  may  be  swept  up  and  saved.  Wood  should 
be  avoided  in  the  making. 

All  crucibles,  tools,  and  anything  else  connected  with  the 
work  are  also  saved,  broken  up,  and  worked  up  afterwards.  If 
these  details  are  looked  after  carefully,  the  loss  in  melting  should 
be  small. 

If  the  bullion  is  to  be  granulated,  it  is  best  done  by  pouring; 
it  into  a  copper  vessel  or  tank  filled  with  ice-cold  water.  Pour 
the  metal  in  with  a  wavy  motion,  holding  the  crucible  3  or  4, 
feet  above  the  surface  of  the  water. 

Small  Amounts  of  Bullion. — Pouring  small  quantities  of  bul- 
lion, whether  it  is  gold  alone  or  an  alloy  of  gold  and  silver,  is- 
generally  unsatisfactory  owing  to  the  difficulty  of  making  a  clean 
pour. 

Very  small  lots  I  prefer  to  melt  in  a  clay  crucible,  which  should 
be  well  glazed  upon  the  inside  with  borax  glass  before  the  bullion 
is  added.  Cover  with  a  good  layer  of  borax  glass  and  a  little  soda>. 
and  keep  the  crucible  covered  until  its  contents  are  perfectly  quiet. 

As  an  extra  precaution  the  small  crucible  can  be  heated  within 
a  larger  one. 

Take  the  crucible  from  the  furnace,  see  that  no  small  globules 
are  on  the  sides,  and  then  allow  it  to  stand  until  it  is  cold.  Break 
the  crucible  and  save  it,  together  with  the  slag,  if  it  is  not  per- 
fectly free  from  metal.  Clean  the  ingot  and  weigh.  If  the  slag; 
is  not  clean,  pulverize,  fuse  it  with  litharge  and  argols,  and  cupel 
the  resulting  lead  button. 


290 


NOTES  ON  ASSAYING. 


RETORTING  AND   CLEANING  MERCURY. 

The  retorts  may  be  large  or  small  and  of  different  shapes. 
When  large,  and  a  large  amount  of  mercury  is  to  be  distilled,  there 
is  always  a  tube  o,  as  in  retort  x,  passing  through  the  cover,  by 
means  of  which  the  mercury  may  be  charged  into  the  retort. 
The  tube  may  be  straight  or  have  a  bend  which  serves  as  a  trap. 


Form  y  is  used  when  small  amounts  are  to  be  distilled. 


The  retort  a  should  be  first  thoroughly  cleaned  and  coated 
on  the  inside  with  chalk,  ruddle  (Fe2O3),  graphite,  or,  better  than 
any  of  these,  lined  with  a  piece  of  paper  put  in  the  bottom  and 
part  way  up  the  sides.  This  will  prevent  the  residue  sticking 
to  the  bottom  of  the  retort,  which  it  is  very  apt  to  do  if  the  heat 
becomes  too  great  or  if  lead  or  zinc  is  present. 

Next  see  that  the  delivery-tube  d,  attached  firmly  to  the 
cover,  is  perfectly  free  and  open.  The  turned  parts  of  the  retort 


METALLURGICAL  LABORATORY  EXPERIMENTS.  291 

and  cover  are  next  cleaned,  and  the  Hg  and  amalgam  put  into 
a.  Mix  some  mineral  paint  or  ruddle  to  the  consistency  of 
thick  cream  and  smear  the  rim  of  the  retort  a  and  rim  of  cover 
b  with  an  even  coating  of  it;  then  place  cover  on  retort,  put 
on  clamp  c,  and  screw  down  firmly.  At  the  Utica  Mine,  Cali- 
fornia, they  use  wood  ashes  (through  30)  mixed  with  water  for 
a  lute. 

The  retort  is  now  ready  to  be  heated.  If  large,  it  is  generally 
heated  over  a  forge  or  in  a  crucible-furnace ;  if  small,  a  good 
lamp  will  do  it.  In  either  case  the  bottom  should  never  be 
heated  above  a  dull  red,  otherwise  it  may  be  softened,  bulged,  or 
melted. 

No  fluxing  material,  like  borax,  should  ever  be  used  in  the 
retort,  for  the  spheroidal  Hg  will  be  changed  to  cohesive,  and 
boil  with  great  violence.  The  residue  might  also  be  found  per- 
manently brazed  upon  the  inside  of  the  retort. 

Mercury  boils  at  674°  F.,  or  357°  C. 

After  lighting  the  lamp  or  fire,  watch  for  the  first  mercury. 
First  comes  the  tremble  of  the  retort  due  to  the  boiling  off  of 
the  moisture.  Next  comes  the  tremble  of  the  retort  due  to  the 
boiling  of  the  Hg,  followed  by  the  hissing  of  the  water  when  the 
hot  Hg  inside  the  tube  comes  in  contact  with  the  cold  water 
outside  the  tube. 

The  accidents  most  likely  to  occur  are : 

1.  The  choking  up  of  the  delivery-tube  d. 

2.  The  blowing  out  of  the  Hg  between  the  retort  and  the  cover. 

3.  Burning  out  of  the  bottom  of  the  retort. 

4.  Adhering  of  the  residue  to  the  bottom  of  the  retort. 

To  avoid  No.  i,  see  that  the  Hg  or  amalgam  is  thoroughly 
cleaned  of  all  dirt  and  sand  before  it  is  put  into  the  retort. 

Rapping  the  delivery-tube  d  with  a  light  hammer  every  now 
and  then  helps  to  keep  it  open  and  clear.  Have  the  pipe  d  well 
rounded  at  bend  and  full  size  all  the  way,  and  give  it  as  much 
slope  as  possible. 

To  avoid  No.  2,  which  is  due  to  tube  d  choking  up  or  to 
poor  luting,  see  that  the  luting  on  of  the  cover  b  is  properly  done 
at  the  start.  If  the  retort  leaks,  a  gray  vapor  will  be  seen  rising 


292  NOTES  ON  ASSAYING. 

above  it.  Test  by  putting  a  piece  of  cold  iron  in  the  blow  for  art 
instant ;  if  it  is  coated  white  (Hg)  there  is  a  leak.  In  such  a  case 
instantly  check  fire  or  put  out  lamp,  cool  down  as  rapidly  as 
possible,  and  avoid  breathing  the  fumes  or  getting  them  into  the 
eyes.  Admit  plenty  of  fresh  air  into  the  room  or  building. 

To  avoid  No.  3,  see  that  the  fire  does  not  become  too  hot. 

To  avoid  No.  4,  see  that  the  retort  is  properly  coated  on  the 
inside. 

Graphite  is  an  excellent  substance  for  luting  and  coating  in 
all  respects  save  one,  and  that  is,  that  the  residue  in  the  retort  is 
difficult  to  melt  together,  unless  nitre  is  used. 

Chalk  and  mineral  paint  do  not  give  this  trouble,  because 
the  borax  glass  used  in  melting  the  residue  in  the  crucible  cleans 
and  joins  the  metallic  particles.  Paper  is,  however,  the  best  for 
the  purpose. 

The  subsequent  melting  of  the  residue  is  done  in  graphite  or 
clay  crucibles  as  described  under  Bullion. 

Any  small  residues  should  be  fused  slowly  in  a  crucible,  to 
allow  any  mercury  to  go  off  gradually.  If  this  residue  is  Ag  or 
Au  or  both,  use  soda  and  borax  glass  as  fluxes.  If  it  is  impure, 
use  in  addition  litharge  and  argols  and  scorify  or  cupel  the 
resulting  lead  button  in  this  case. 

Scorification  is  dangerous,  owing  to  danger  of  spitting,  if  any 
mercury  is  left  in  the  residue.  If  attempted,  the  heating  shoul  1 
be  very  gradual  and  another  scorifier  used  as  a  cover. 

Melting  lead  in  the  retort  to  collect  residue,  as  recommended 
in  some  books,  I  have  never  found  a  success. 

To  clean  the  mercury  and  put  it  in  good  condition,  first  wash 
with  a  stream  of  H2O  to  remove  all  soluble  and  light  material,, 
stir  with  porcelain  spatula,  and  pour  frequently  from  one  vessel 
into  another.  Do  not  touch  with  the  hands.  Decant  off  water 
and  add  a  small  piece  of  potassium  cyanide  (poison),  which  ought 
to  clean  it  nicely.  Wash  again  with  water,  when  the  Hg  should 
be  perfectly  clean.  Most  of  the  water  is  then  removed  with  a. 
sponge  and  the  last  of  it  by  means  of  blotting-paper.  Dry  and 
weigh.  Vessels  for  holding  it  should  be  strong,  solid,  and  perfectly 
free  from  all  oil  or  grease. 


METALLURGICAL   LABORATORY  EXPERIMENTS. 


293 


Large  amounts  of  mercury,  having  been  cleaned  with  KCN 
and  washed  with  water,  can  be  further  purified  in  the  following 
way: 

Pour  the  entire  quantity  through  a  funnel,  either  perforated 
itself  or  else  with  a  chamois  tied  over  the  end  of  the  stem,  and 
allow  it  to  fall  as  a  spray  through  some 
acid  as  in  b.  From  there  it  runs  off  by 
tube  e  into  the  iron  mercury  flask  a.  It  is 
then  both  clean  and  almost  dry,  for  its 
weight  forces  any  acid  or  water  out. 

If  the  Hg  has  been  distilled  from  tin  or 
zinc,  the  acid  used  is  one  part  HC1  and  one 
part  water. 

If  distilled  from  lead,  use  one  part  HNO3 
and  four  parts  water  in  tube  b. 

Small  quantities  may  be  strained  through 
chamois  into  a  vessel  containing  the  acid ;  it 
is  then  washed  and  dried.  Hg  containing 
small  amounts  of  Pb  or  Zn  distils  more 
slowly  than  when  these  are  absent,  and  it  is 
difficult  to  free  the  Hg  entirely  from  them. 
Blowing  air  into  Hg  also  cleans  it.  One 
writer  speaks  of  covering  the  Hg  in  the  retort  with  cinnabar,  iron 
filings,  or  lime,  according  to  the  impurities  present.  The  sulphur 
in  the  cinnabar  combines  with  the  base  metals,  iron  combines 
with  As,  forming  a  speiss,  and  the  lime  will  take  out  the  sul- 
phur. A  layer  of  charcoal  in  the  retort  is  also  said  to  purify  the 
mercury. 

MUFFLE   CHLORIDIZ1NG   ROAST   OF    SILVER   ORES. 

This  process  is  applicable  to  ores  which  are  not  "free  mill- 
ing," i.e.,  ores  which  cannot  be  directly  amalgamated.  The  ob- 
ject of  the  test  is  to  determine,  from  a  given  quantity  of  the  ore 
to  be  experimented  with — 

i st.  What  amount  of  silver  is  lost  or  volatilized  during  the 
roast.  (If  the  ore  contains  gold  see  A,  I.  M.  E.,  Vol.  XVII,  as 
to  loss  in  roasting.) 


294  NOTES  ON  ASSAYING. 

2d.  Percentage  of  soluble  salts  in  roasted  ore. 
3d.  Percentage  of  silver  as  sulphate  in  roasted  ore. 
4th.  Percentage  of  silver  salts  soluble  in  hyposulphite  of  soda 
solution. 

5th.  Percentage  of  silver  salts  soluble  in  extra  solution. 
The  ores  met  with  may  be  divided  into  three  groups: 

(a)  Heavily  sulphuretted  ores,  which  in  some  cases  have  ta 
be  roasted  a  long  time  previous  to  the  addition  of  salt. 

(b)  Slightly  sulphuretted  ores. 

(c)  Ores    carrying  a   very  small  quantity  of    sulphides,  the 
sulphurets  being  present  in  so  small  an  amount  that,  in  some 
cases,  it  is  found  necessary  to  add  sulphur  or  iron  pyrites  in  order 
to  decompose  the  salt  and  liberate  chlorine.     The  percentage  of 
salt  added  varies.     (At  Aspen,  Colo.,  it  is  claimed  that  by  using- 
10  to  15%  the  amount  of  silver  volatilized  is  diminished.)     With 
some  ores  it  is  found  better  to  add  the  salt  at  the  beginning, 
with  others  at  the  end  of  the  roast.     Ores  containing  no  A  s,  Sb, 
Pb,  or  Ca  are  generally  best  treated  by  adding  the  salt  at  the 
beginning.     If  A  s  volatilizes  as  a  sulphide,  the  loss  of  silver  seems, 
to  be  smaller  than  if  it  volatilizes  as  a  chloride.      Lead  and  lime 
should,  if  possible,  be  kept  as  sulphates, -for  otherwise  they  are 
great  consumers  of  chlorine. 

Suppose  an  ore  carries  sulphides  of  lead,  zinc,  and  iron.  It 
is  roasted  for  a  long  time,  at  a  very  low  heat,  in  order  to  form 
sulphates  of  lead,  zinc,  and  iron.  The  last  will  decompose  salt 
with  the  formation  of  chlorine,  the  other  two  sulphates  will  not. 
Therefore  we  wish  to  form  FeSO4  and  as  much  sulphate  and 
oxide  of  lead  and  zinc  as  possible  and  yet  not  decompose  the 
FeSO4.  For  this  reason  we  must  keep  the  heat  low  and  roast 
slowly,  otherwise  the  FeSO4  will  be  broken  up  before  all  of  the 
PbS  and  ZnS  are  converted  either  into  sulphates  or  oxides.  When 
we  think  this  point  has  been  reached  the  salt  can  be  added. 

The  sulphates  are  decomposed  by  heat  in  the  following 
order:  sulphate  of  iron,  sulphate  of  copper,  sulphate  of  silver,  the 
last  commencing  to  decompose  at  a  red  heat.  Sulphate  of  zinc 
is  decomposed  with  difficulty;  sulphates  of  lead  and  lime  are  not 
decomposed  by  heat  unless  much  silica  is  present.  The  first  three 
sulphates  will  all  decompose  salt  and  are  therefore  chloridizers : 


METALLURGICAL  LABORATORY  EXPERIMENTS.  295 

2NaCl+  FeSO4  =Na2SO4+FeCl2; 
2NaCl  +  CuSO4  =Na2SO4+CuCl2; 
2NaCl-h  Ag2SO4  =  Na2SO4+  2AgCl; 
4NaCl+  2FeSO4+  3O  =  4C1+  2Na2SO4+Fe2O3. 

These,  together  with  the  HC1  formed,  chloridize  the  ore: 

Steam  +  CuCl2  =  CuO  +  2HC1  ; 
2HCl+Ag2S  =  2AgCl+H2S. 

Students  should  make  careful  note  of  the  duration  of  roast, 
heat  used,  and  at  what  time  the  salt  was  added.  The  following 
reactions  may  also  take  place,  among  a  great  many  others  : 

SO2  +  O  =  SO3.     SO3  +  2NaCl  +  H2O  =  Na2SO4  +  2HC1  ; 
Fe2Cle+3O  =  Fe2O,+  6Cl.     Heat  upon  2CuCl2  =  Cu2Cl2+2Cl;    ; 


Cu2S  +  FeS2+6NaCl+i20=FeCl2+2CuCl2+3Na2S04. 

Testing  an  Ore.  —  Crush  ore  through  a  30-  or  4o-mesh  sieve. 
Sample  carefully  and  crush  sample  for  assay  through  a  xoo-mesh 
sieve.  Take  5  grammes  and  assay  (all  assays  in  this  work  should 
be  made  by  crucible}.  Calculate  both  the  per  cent  of  silver  in 
the  ore  and  the  ounces  per  ton. 

Weigh  out  from  2  A.T.  to  200  grammes  of  ore  (through  a  30-  or 
4o-mesh  sieve)  on  pulp-balance  and  roast  in  a  clay  dish  with  from 
3  to  10%  of  salt.  Have  the  furnace  only  one  third  full  of  coke 
and  the  bottom  of  muffle  just  red  at  first,  to  prevent  caking.  Stir 
the  ore  every  now  and  then  and  roast  it  from  30  minutes  to  2  hours 
at  a  low  heat.  Never  have  the  muffle  near  a  scorifying  tempera- 
ture, but  the  ore  just  red.  After  roasting,  sift  it  through  the  same 
sieve  as  before  and  WEIGH  on  the  pulp-balance.  Sample  care- 
fully, take  enough  ore  for  the  following  tests,  and  grind  in  an 
agate  or  porcelain  mortar  through  a  loo-mesh  sieve.  (It  will  take 
about  25  minutes  to  grind  80  grammes  through  a  loo-mesh 
sieve.)  If  iron  was  used,  we  might  have  (2AgCl+Fe  =  FeCl2-f 
2Ag),  and  the  latter  is  not  readily  soluble  in  hyposulphite. 

Take  5  grammes  and  assay.  Calculate  the  per  cent  of  Ag  and 
find  total  amount  in  roasted  ore.  Difference  between  this  and 
total  Ag  in  raw  ore  =  silver  volatilized  during  the  roast. 


296  NOTES  ON  ASSAYING. 

Soluble  Salts  (i.e.,  the  excess  of  NaCl  used  and  all  chlorides 
and  sulphates  soluble  in  H2O  and  the  AgCl  soluble  in  the  NaCl 
solution  if  an  excess  was  used  in  the  roast). — Weigh  5  grammes 
and  leach  by  decantation  with  hot  H2O,  until  neither  AgNO3 
nor  ammonium  sulphide  give  a  precipitate.  Dry,  burn  the  filter, 
and  weigh. 

Loss  =  soluble  salts. 

As  the  percentage  of  NaCl  used  in  the  roast  increases,  the 
soluble  salts  generally  increase. 

Silver  as  Sulphate  and  Silver  Salts  Soluble  in  Water  containing 
Salt  (NaCl). — Assay  the  whole  residue  after  leaching  with  water. 
The  difference  between  this  weight  and  the  weight  of  the  silver 
button  in  5  grammes  of  roasted  ore  equals  the  Ag2SO4  and  other 
silver  salts  soluble  in  water  or  in  a  brine  solution,  for  it  must  be 
remembered  that  if  a  large  excess  of  NaCl  is  used  in  the  roast,  we 
will  have  a  strong  brine  solution,  in  which  AgCl  is  soluble  to  a 
certain  extent.  If  any  NaCl  is  left  undecomposed  in  the  ore,  the 
Ag2SO4  cannot  be  determined,  for  it  will  be  broken  up  by  the 
excess  of  NaCl,  and  the  AgCl  precipitated.  This  may,  however, 
go  into  solution  again  on  standing  if  the  brine  is  sufficiently  strong. 

Silver  Salts  Soluble  in  Hyposulphite. — Place  J  A.T.  of  ore  in  a 
beaker;  add  300  c.c.  of  hot  water,  decant  H2O,  and  then  treat 
with  about  250  c.c.  of  a  5%  solution  of  hypo,  (allow  hypo,  to  stand 
on  ore  for  say  \  hour  at  about  125°  F.  and  stir  it  frequently): 

2  AgCl  +  2Na2S2O3  =  2NaCl+  2NaAgS2O3. 

Filter  by  decantation,  wash  several  times  with  water,  and  finally 
wash  with  a  little  fresh  hypo.  The  soluble  silver  salts  should 
now  be  all  removed  and  the  last  washing  show  no  turbidity  on 
the  addition  of  ammonium  sulphide  unless  lead  salts  are  present. 
(PbCl2  is  not  readily  soluble  in  hypo.,  but  PbSO4  is;  so  if  much 
of  the  former  salt  is  present,  a  precipitate  of  lead  sulphide  may 
be  obtained  after  many  washings.)  Dry  residue,  weigh,  and 
assay  the  whole  of  it.  The  difference  between  this  and  the  assay 
of  the  roasted  ore  gives  the  amount  of  silver  soluble  in  water  and 
hyposulphite.  Subtract  the  silver  salts  soluble  in  water  and  we 
obtain  the  AgCl  and  the  silver  salts  soluble  in  hypo. 


METALLURGICAL  LABORATORY  EXPERIMENTS.  297 

Silver  Salts  Soluble  in  Extra  Solution. — This  is  the  Russell 

process  and  consists  in  the  treatment  of  the  roasted  ore  with 
cuprous  hyposulphite  solution:  2\  parts  Na2S2O3+5H2O  and  i 
part  CuSO4+5H2O.  When  made  in  this  way,  no  cuprous  hypo- 
sulphite will  come  down.  The  solution  should  be  fresh  and 
should  contain  a  slight  amount  of  free  H2SO4.  If  heated  above 
85°  C.  it  decomposes,  and  at  boiling,  Cu2S  separates  out.  Silver, 
Ag2S,  and  the  antimonial  and  arsenical  minerals,  like  ruby  silver , 
and  stephanite,  are  soluble  in  this  solution,  whereas  all  these, 
with  the  exception  of  the  silver,  are  insoluble  in  the  hyposulphite 
alone : 

4Na2S2O3+ 3Cu2S2O3+  3Ag2S  =  3Cu2S  +  6NaAgS2O3+ Na2S2O3. 

The  manner  in  which  ores  are  treated  with  the  extra  solution 
of  course  may  vary  with  the  ore  (see  Lixiviation  of  Silver  Ores 
with  Hyposulphite  Solutions  by  Stetefeldt),  but  the  following  pro- 
cedure will  generally  answer: 

Take  JA.T.  of  ore  and  treat  it  with  hot  water  as  before. 
Decant  off  the  solution  and  add  60  c.c.  of  H2O  and  12.5  grammes 
of  hyposulphite  of  soda.  Let  it  stand  30  minutes  to  one  hour. 
Add  25  c.c.  of  copper  solution  (200  grammes  CuSO4  in  1000  c.c. 
of  water)  and  dilute  with  cold  water  to  300  c.c.  and  heat  not 
above  110°  F.  for  about  10  minutes.  Filter,  wash  with  H2O, 
dry,  weigh,  and  assay.  The  difference  between  the  weight  of 
silver  obtained  from  this  and  that  obtained  from  the  hypo,  test 
gives  the  silver  salts  soluble  in  the  extra  solution  and  those  not 
soluble  in  hypo,  alone. 

If  the  ore,  as  received,  has  been  previously  roasted,  it  may  be 
damp,  owing  to  its  having  taken  on  moisture,  due  to  the  NaCl  and 
other  chlorides.  In  this  case  dry  it,  sample  carefully,  take  200 
to  250  grammes  and  proceed,  as  given  above,  with  the  determina- 
tion of  "Soluble  Salts." 

Each  student  should  make  out  a  complete  report  similar  to  the 
one  on  page  298. 


2  9  8: 


NOTES  ON  ASSAYING. 


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METALLURGICAL  LABORATORY  EXPERIMENTS.  299 

The  results  a,  b,  c,  and  d,  also  a,  b,  e,  and  /  should  foot  up 
100  per  cent,  and  are  all  based  upon  the  total  silver  in  the  raw 
ore  or  (#). 

The  amount  of  silver  in  the  ore  after  leaching  with  water, 
that  is  .6689  grammes,  can  be  obtained  by  either  of  the  proportions : 
5  :  226  ::  .0148  :  x  or  4.56  :  206.12  ::  .0148  :  x. 

The  amount  of  silver  in  the  ore  after  leaching  with  hypo,  and 
the  extra  solution  can  be  obtained  in  the  same  way. 

The  tailings,  after  leaching  with  the  extra  solution,  assay  7.7 
oz.  per  ton.  The  salts  soluble  in  the  extra  solution  =16.05%. 
If  the  original  ore  was  very  rich  in  silver  the  percentage  of  silver 
salts  removed  by  the  process  would  have  to  be  takei  into  con- 
sideration, but  as  the  per  cent  of  silver  in  this  ore  was  only  .4%, 
the  silver  salts  soluble  in  this  extra  solution  may  be  disregarded 
in  the  present  calculation.  Therefore  if  the  tailings  which  assay 
7.7  oz.  contained  this  16%  of  other  salts,  they  would  assay  lowerv 
and  to  obtain  this  value  we  make  the  proportion  of 

100—16.05  :  I0°  ::  x  :  7-7  > 
that  is,  #  =  6.5  oz. 

The  application  of  this  calculation  is  brought  out  more  clearly 
in  the  next  test,  Pan  Amalgamation. 

Going  Back  or  Decrease  in  the  Chlorination. — Some  roasted 
ores  when  leached  directly  with  hypo,  show  a  higher  extraction 
or  chloridization  than  if  leached  with  H2O  and  then  with  hypo. 
This  is  said  to  be  accounted  for  as  follows  (see  paper  by  W.  S. 
Morse,  A.  I.  M.  E.,  Oct.  1895) :  AgCl  is  soluble  in  brine,  i.e.,  in. 
H2O  used,  plus  the  excess  of  NaCl  left  in  the  roasted  ore.  If  the- 
ore  contains  unroasted  sulphides,  say  ZnS,  not  decomposed  in  the- 
roast,  we  may  have  2AgCl+ZnS  =  Ag2S  +  ZnCl2  or  2AgCl  +  PbS  = 
Ag2S  +  PbCl2.  That  is,  the  silver  in  solution  has  gone  back  to 
Ag2S,  which  is  not  soluble  in  hypo,  alone,  but  is  soluble  in  the 
extra  solution. 

EXAMPLE. — Ore  containing  29  oz.  silver  and  about  2.8%  zinc^ 
Ore  leached  with  hypo,  directly  showed  78  ..92%  of  silver  soluble. 
Ore  leached  with  H2O  and  then  with 
hypo,  showed  64.32%  "      " 


Silver  gone  back  to  Ag2S  =    14 . 6% 


300  NOTES  ON  ASSAYING. 

This  same  ore  treated  with  the  extra  solution  showed  89%  of 
the  silver  soluble. 


PAN   AMALGAMATION   OF   SILVER  ORES. 

Silver  ores,  for  amalgamation,  are  divided  into  two  classes: 

1.  Free-milling  ores,  or  those  that  require  no  roasting,  such 
as  chloride,  bromide,  iodide,  and  sulphide. 

2.  Refractory  ores,  or  those  that  require  a  chloridizing  roast 
with  salt  previous  to  amalgamation. 

Whether  the  ore  is  raw  or  roasted,  it  should  be  sampled  care- 
fully, after  grinding  it  through  a  30-  or  4o-mesh  sieve.  If  the 
•ore  contains  AgCl,  avoid  the  use  of  iron  for  grinding,  if  possible, 
for  2AgCl+Fe  =  FeCl2+2Ag.  Assay  by  crucible  method  and 
•calculate  both  the  per  cent  of  silver  and  of  the  gold  in  the  ore 
and  the  ounces  per  ton.  Determine  the  per  cent  of  soluble  salts 
and  the  per  cent  chloridized  as  per  notes  on  "Muffle  Chloridizing 
Roast."  Weigh  out  2  kilos  of  ore,  if  small  pans  are  to  be  used. 
(Large  pans  are  iron;  small  pans  are  either  iron  or  copper.) 
The  pan  is  next  cleaned  out  and  then  set  in  motion;  add  suffi- 
cient water  to  cover  the  miiller,  the  latter  being  so  set  as  to 
grind  upon  the  dies,  unless  a  copper  pan  is  used.  The  ore  is 
then  added  until  the  pan  is  charged  (the  small  pans  take  about 
1800  grammes).  The  contents  should  be  about  the  consistency 
of  thick  paint,  and  they  will  probably  require  the  addition  of 
more  water  to  make  them  so,  but  it  is  better  to  have  the  pulp 
too  thick  than  too  thin. 

Unless  a  copper  pan  is  used  or  the  ore  has  been  roasted,  the 
miiller  should  grind  on  the  dies  until  the  ore  is  entirely  free  from 
lumps.  If  all  the  ore  will  pass  a  40- mesh  sieve,  grinding  is  unneces- 
sary. When  the  pulp  is  sufficiently  fine,  raise  the  miiller  (to  avoid 
grinding  or  "flouring"  the  Hg)  and  then  add  200  to  500  grammes 
of  Hg  in  a  fine  spray.  This  can  be  done  through  chamois  or  by 
means  of  a  funnel  drawn  to  a  fine  point. 

If  the  pulp  is  in  the  right  condition,  mercury  will  be  found 
in  every  portion  of  it.  Heat  the  pulp  to  about  160°  to  180°  Fah. 
.and  keep  this  temperature  up  to  the  end  of  the  test.  Amalgamate 


METALLURGICAL   LABORATORY  EXPERIMENTS,  301 

for  from  one  to  three  hours  and  try  to  keep  the  pulp  of  the  same 
consistency  all  the  time.  Many  reactions  take  place  which  may 
be  due  to  the  constituents  of  the  ore  or  may  arise  from  the  chemi- 
cals, such  as  salt,  blue  vitriol,  or  H2SO4,  which  have  been  added 
to  the  pulp.*  Much  uncertainty  exists  in  regard  to  these  reac- 
tions, but  the  following  are  said  to  take  place: 

CuSO4  +  2NaCl  =  CuCl2+  Na2SO4  ; 
Cu2Cl2+  Ag2S  =  2AgCl  +  Cu2S  ; 
2CuCl2+  Ag2S  =  2AgCl+  Cu2Cl2  +  S  ; 
2CuCl2+  2Ag  =  2AgCl+  Cu2Cl2; 
Cu2Cl2  +  Ag2S  =  2  Ag  +  CuS  +  CuCl2  ; 


The  iron  pan  aids  the  action  of  the  mercury,  and  decom- 
poses both  the  AgCl  and  any  calomel  that  may  form. 

PbCl2  will  amalgamate,  but  PbSO4  will  not,  and  this  is  one 
reason  for  adding  CuSO4  when  lead  is  present  in  an  ore.  When 
zinc  blende  and  pyrite  are  present  and  the  gangue  is  calcareous, 
some  authorities  say  that  salt  and  bluestone  should  not  be  added 
to  the  pan.  The  lime  consumes  the  bluestone,  forming  CaSO4, 
and  the  sulphides  seem  to  flour  the  mercury  in  the  presence  of 
salt  and  perhaps  form  chlorides.  CuCl2  or  Fe2Cl6,  if  present  in 
too  large  proportion;  are  liable  to  form  calomel  (Hg2Cl2).  To 
discharge  the  small  pan,  either  fill  it  with  water  and  run  the 
whole  contents  into  a  hydraulic  classifier  or  else  pan  it  down  in 
a  gold-pan.  All  the  water,  slimes,  and  tailings  are  either  filtered 
on  a  large  cloth  filter,  stretched  on  a  wooden  frame,  or  allowed 
to  settle  overnight  and  the  water  decanted  the  next  day.  Dry 
the  residue,  weigh,  pass  through  a  sieve  to  remove  the  lumps, 
sample  carefully,  and  assay.  The  mercury  and  amalgam  are 
cleaned  and  retorted.  (See  Retorting.)  As  some  amalgam  will 
stick  to  the  pan  and  muller,  or  some  amalgam,  from  a  previous- 

*  Patio    Process    for    Amalgamation  of  Silver   Ores.      Manuel  V.  Ortega, 

American  Institute  Mining  Engineers,  November  1901. 


302 


NOTES  ON  ASSAYING. 


run,  may  be  removed,  results  must  be  based  on  the  assay  of  the 
tailings. 

The  residue  in  the  retort  is  melted  in  a  small  crucible  with 
.a  little  soda,  borax  glass,  and  lead,  and  the  button  cupelled,  unless 
copper  is  present,  when  the  button  will  have  to  be  scorified  until 
the  copper  is  removed. 

Weigh  the  resulting  button  and,  if  gold  is  present,  part  as 
usual. 

The  report  should  be  as  follows: 


Weight 
of  Ore. 

Assay. 

Total 
Weight 
of  Ag 
in 
Grms. 

Per 
Cent 
Chlorid- 
ized. 

Per 
Cent  as 
Ag2S04 

Per 
Cent 
In 
Tail- 
ings. 

Raw  ore    .                       ... 

Roasted  ore.                

1710  gm. 

106  4  oz. 

6  24.0 

Tests  on  the  roasted  ore  showed 
that: 
Salts   soluble  in  H2O  =  8.9i% 
^Sample  of  roasted  ore  lixiviated 
with  hypo,  showed 
Soluble  salts  =  9  .  2% 
Based   on    these   results,   the 
whole    roasted    ore,    after 
hypo,  leach,  would  be  

1553  gm. 

19.8  oz. 
19.8  oz. 

1.054 

79.1 

3.98 

16.92 

:Silver  extracted 5 . 186 

Tailings,  calculated  from  salts 

soluble  in  water  =  1558  gm. 

Actual    tailings,   after  amalga- 

mation=  1523.4"     23.2OZ.      1.21 

^Bullion  recovered 4-42 

Unaccounted  for.  .  .61 


•83.11%       16.89 


70.83% 
:   9.78% 


19-39 


Mercury 


Weight  Taken. 
500  grammes 


Recovered. 
490  grammes 


Per  cent  Lost. 
2 


In  practice  it  is  not  possible  to  weigh  the  tailings  from  a  proc- 
ess, but  it  is  possible  to  weigh  both  the  raw  and  roasted  ore  and 
to  obtain  the  assay  of  these.  It  is  also  possible  to  obtain  a  sample 
of  the  tailings  as  they  go  to  waste,  and  from  these  results  calcu- 
late the  true  extraction. 

If  the  process  is  pan  amalgamation,  the  assay  of  the  roasted 
ore  is  obtained  and  the  percentage  of  salts  soluble  in  water.  If 
a  leaching  process  is  used,  the  roasted  ore  is  assayed  and  the 
salts  soluble  in  the  solvent  used  are  determined.  A  fair  sample 


METALLURGICAL   LABORATORY  EXPERIMENTS.  303 

of  the  tailings  as   they  are  discharged  from  the  pan,  settler,  or 
leaching-tank  is  taken  and  assayed. 

Now  this  assay  must  be  higher  than  it  would  be  if  the  salts, 
other  than  silver  salts  (the  percentage  of  these  may  be  neglected 
unless  the  ore  is  extremely  rich)  soluble  in  water,  were  still  present 
in  the  tailings  or  waste;  in  other  words,  the  tailings  have  been 
partly  concentrated. 

Take  the  previous  test  for  example;  the  tailings  after  amalga- 
mation assay  23.2  oz.  and  the  salts  soluble  in  water  =  8. 91%. 

Therefore,  100  —  8.91  :  100  ::  oc  :  23.2;  that  is,  #=21.13  oz. 

If  the  roasted  ore  assayed  106.4  oz.,  then  the  bullion  recovered 
should  be 

106.4  —  21.13 
106.4 


=  80.1%., 


The  actual  bullion  recovered,  based  on  the   percentage  of 
•silver  left  in  the  tailings  (19.39%),  was  80.61%,  which  corresponds 

•  TXNI-^T    /"» l^oiil^r 


very  closely. 


INDEX. 


Acid  slag,  8,  9 

Active  fluxes,  89 

Alkaline  carbonates,  7 

Alkali  or  alkali  wash,  268 

Alloys  of  silver  and  copper,  cupella- 
tion  of,  204 

Amalgam,  gold,  286 
silver,  285 
making,  284 

Amalgamation  in  ball  mill,  279 
by  bottle,  277 
of  gold  ores,  283 
by  pan,  277 
by  stamp-mill,  283 

Annealing-cups,  154 

Antidote  for  KCy  poisoning,  269 

Antimonial  ores  for  silver,  45,  122 

Antimony,  reactions  in  cupellation, 

59 
Argols,  6,  71,  83,  85 

fusion  for  reducing  power,  83, 

84 

Arseniate  of  soda  and  iron,  70 
Arsenite  of  soda  and  iron,  71 
Arsenical  ores,  crucible  assay  for  gold 

and  silver,  136 
scorification  for  silver, 

45 

Assaying,  definition,  i 

Assaying  solutions,  183 

Assay  of  ores  for  copper,  213 
gold,  127 
lead,  190 
platinum,  224 
silver,  39,  86 
tin,  219 

Assay  reagents,  5 

Assay  ton  system,  3 

Balances,  2 

Ball  mill  amalgamation,  279 

Barite,  flux  for,  73,  124 


Barite  ores,  assay  of,  124 
Barrel  chlorination,  252 
Base  bars,  198 
Base  bullion,  199 
Basic  slag,  8,  9 
Bicarbonate  of  soda,  66 

influence  on  re- 
ducing power, 

84,97 

Bismuth,  47 
Black  flux,  194 

substitute,  194 
Bleach  ing-powder,  255 
Blicking,  56,  57 
Bone  ash,  analysis,  20 

on  the  market,  20 
Borax,  68,  85 

influence  on  R.P ,  86,  96 
Borax  glass,  68,  85 

influence  on  R.P.,  86 
in  scorification,  44 
Bottle  amalgamation,  277 
Broad  spatula,  30 
Brightening  of  button,  56,  57 
Brittle  buttons,  42,  47,  91,  197 
Bromine,  treatment  of  gold  ore  by, 

272 

Bromide  of  cyanogen,  275 
Bucking-board,  cleaning  of,  31,  32 
Bullion,  198 

assay  of,  199 
base,  199 
gold,  210 

assay  of,  211 
melting  and  refining,  286 
pouring  and  casting,  288 
silver,  198,  201,  205 
assay  of,  201 
Gay-Lussac   method, 

199 

results,  203 
Volhard's  method,  207 
305 


,3°6 


INDEX. 


.Bullion,  silver,  wet  methods,  207 
small  amounts,  289 
toughening,  288 


Calcining,  244 

Carat,  5 

Charcoal,  6,  7,  71,83,85 

fusion  for  reducing  power, 

83,  85 
Charge     (crucible)    for    silver    and 

gold  in  ores: 
chromite  ore,  129 
cupriferous  ores,  118,  119 
hematite,  93,  129 
iron  oxide,  89,  93,  129 
limestone,  89,  129 
oxides,  88,  89,  129 
roasted  ores,  129 
silicious  ores,  88,  92,  129,  130 
sulphide  ores,  103,  106,  109,  no, 

.  "i>  139 
Chiddey's,  A.,  method  for  assaying 

cyanide  solutions,  186 
Chloridizing  roast,  245,  293 
Chlorination,  barrel,  252 

of  gold  ores,  245 
Plattner,  245 

Chromite,  assay  for  gold,  129 
Clays,  analysis  of,  12 
Clays,  fusion  of,  75 
Cleaning  bucking-board,  32 
Cleaning    button    before    weighing, 

58 

Cobalt  ores  for  silver,  45 
Color  of  cupels  after  using,  57 
Color  of  scorifiers  after  using,  46 
Color  of  slags,  9,  91 
Color  of  vapors,  41 
Combination  wet  and   dry  method 

for  gold,  181 
Combination  wet  and   dry  method 

for  silver,  54 
Concentration  test,  35 
Coning  and  quartering,  27,  28 
Copper  assay  for  silver,  combination 

wet  and  dry  method,  54 
Copper,  influence  on  loss  of  gold  in 

cupelling,  161 
reactions  in  cupellation,  59 
in  scorification,  43 
Copper  bars,  assay  for  gold,  180 
assay  for  silver,  53 


Copper  bars,  combination  wet  and 
dry  method  for  gold, 
181 

combination    wet    and 
dry  method  for  silver, 

54. 
Copper  matte,  10,  45,  49,  180 

assay  for  gold,  180 
silver,  49 
scorification  effect  of 

borax,  51,  52 
scorification  effect  of 

glass,  51,  52 
scorification  effect  of 

silica,  51,  52 

Copper  ores,  assay  for  copper,  213 
classification,  213 
crucible  fusion  for  sil- 
ver, 118 

effect    of    different    re- 
agents, 121 
fusion  of,  215 
native,  217 
oxide,  217 
purchase  of,  218 
roasting  of,  215 
scorification,  45,  49 
sulphide,  214 
Cornish  method,  28 
Cream  of  tartar,  6,  71,  216 
Crucible  method: 
copper  ores,  216 
gold  ores,  Class  I,  1 29 
II,  131 
II,  iron     method, 

I31,  T33 
II,  F,  139 
silver  ores,  86 

Class  I,  88 

II,  93,  I03 
iron  method,  109 
special  methods,  118 
tin  ores,  219 
Crucibles,  15 

analyses,  16 
glazing  of,  16 
graphite,  16 
Hessian,  16 
number  in  cask,  17 
properties  of,  15 
size  of,  1 6,  17 
using  a  second  time,  16 
Crust  on  fusion,  85 


INDEX 


307 


Crystals  of  litharge,  56,  65 
Cupellation,  55 

of  gold,  1 60 
of  silver,  56 
reactions  in,  58,  59 
silver  losses  in,  62 
Cupels,  20 

assay  of,  60,  170,  177 
color  after  using,  57,  63,  161 
drying,  21 
manufacture,  21 
using  only  once,  22 
Cyanide  process: 
alkali  wash,  268 
as  applied  to  concentrates,  262 
experimental  treatment  of  ores,  258 
some  reactions,  267 
report  on,  260 

for  treatment  of  ores,  256,  260 
Cyanide  solutions,  assay  of,  183,  186 
Cyanogen  bromide,  275 

Dead  roast,  133,  158,  214 
Desulphurizing  agents,  7 ' 
Dusting  of  ores,  117 

JExperiment,  barrel  chlorination,  252 
bottle       amalgamation, 

277 

in  concentration,  35 
cyanide  process,  258 
pan  amalgamation,  300 
Plattner  process,  245 
roasting  an  ore,  157 
roasting      concentrates, 

.  J57 
silver  chloridizing  roast, 

.293 

with  bullion,  200 
with  C.P.  silver,  59 
Experimental  treatment  of  gold  ores, 
276 

*'  Fan  "  from  vanning,  134 
Ferric  oxide,  6,  72 

action  in  fusion,  73 
Ferrous  sulphate  solution,  251 
Final  sample,  fineness,  26,  30,  164 
Fine  silver  bars,  198 
Fire-brick,  12 

fusing-point,  12 

laying,  23 
Fire-clays,  12 


Flour,  6,  71,  113,  125,  149 

Fluor-spar,  73,  192 

Fluxes,  8,  66 

Fluxes,  active,  89 

Flux  mixture,  113,  125,  149 

Free-milling  gold  ore,  276 

true  value,  278 

Free-milling  test  in  ball  mill,  279 
Freezing  of  button  in  cupelling,  56 
Fuels,  ii 
Furnaces,  n,  13,  14 

repairing,  23 
Fusion,  how  made  in  pot-furnace,  83, 

90,  135 
in  muffle,  92,  115,  130,  131, 

142,  193,  194 
in  muffle,  how  made,  193 
Fusion  products,  9 

Galena,  assay  for  silver,  in 
Glass,  73,  84 

influence  on  reducing  power 

of  a  substance,  84,  85 
Gold,  combination     wet     and     dry 

method,  181 
flashing  of,  156 
fusing-point,  127 
how  paid  for  in  ores,  156 
in  bismuth,  183 
in  copper  bars,  180 
in  copper  matte,  180 
in  star  antimony,  182 
in -zinc-box  residues,  163 
loss  in  cupelling,  160,  161,  164 
parting  buttons,  151 
precipitation  from  AuCi?,  248, 

250 

effect  of  impurities  upon  pre- 
cipitation, 251 
separation    from    Pt   and   Ir, 

157^231 
solubility  in  strong  nitric  acid, 

152,  162 
solubility  in  nitrous  and  nitric 

acid  combined,  181 
value  of  grain,  5 

gramme,  5 
ounce-,  4 

volatility  of,  159,  160 
weighing  of,  155 
Gold  amalgam,  286 
Gold  bullion,  210 

minerals,  rich  ores,  128 


3o8 


INDEX. 


Gold  ores,  127 

crucible  method,  129 
experimental      treatment, 

276 

fusion  in  muffle,  130 
methods  of  assay,  128 
scorification  method,  128 
steps  in  assay,  128 
Gold-pan  amalgamation,  277 
Gold  precipitate,  cupellation  of,  248 
Gold  solutions,  assay  of,  183 
Granulated  lead,  8,  80 

correction  tor  silver, 

47 

testing  for  silver,  80 
Graphite,  analysis,  16 
Graphite  crucibles,  17 

heating  of,  17 
manufacture    of, 
18 

Hammer  and  anvil,  58 

Hard  buttons,  42,  91,  197 

Heath,  G.  L.,  copper  assaying  in  Lake 

Superior  Region,  218 
Hematite,  assay  for  gold,  129 

silver,  93 

Inquartation,  152 
Introduction,  i 
Iridium,  224,  226,  232,  239 
Iridosmium,  224,  231,  232,  242 
Iron,  7,  70 

removal  from  fusion,  91 
when  necessary  in  fusion,  in 
Iron  and  arseniate  of  soda,  70 
Iron  and  arsenite  of  soda,  71 
Iron  and  lead  silicates,  70,  192,  196 
Iron  and  lead  sulphide,  7,  70,  74, 192 
Iron  and  litharge,  6,  70,  74 
Iron  matte,  10,  n 
Iron  method,  109,  133,  135 

advantages,  135 
disadvantages,  135 
fusion,  135 
reactions,  no 
when  used,  in,  112 
Iron  oxide,  assay  for  gold,  1 29 
silver,  93 

best  flux  for,  75,  76 
fusion  oi,  89 

influence  on  size  of  lead 
button,  73 


Iron  speiss,  10,  137,  138 
Jewellers'  sweeps,  45 


Labelling  samples,  25 
Lead,  190 

amount  required  in  scorifica- 
tion, 45 

assay  of  ores  for,  190 
granulated,  80 

testing   for   silver, 

80 
ratio  to  copper  in  scorifying, 

51,52 

Lead  and  nitre,  72   . 
Lead  assay,  fusion  in  muffle,  193 

fusion    in     pot-furnace, 

194 

general  remarks,  197 
iron  crucible  method,  195 
KCN  method,  194 
other  metals  in,  192 
oxide  ores,  195 
slags,  195 
sulphide  ores,  192 
Lead  bullion,  199 
Lead  button,  size  to  cupel,  22 

size  from  scorification, 

46,  56 
size  from  crucible  work, 

81,  109,  116 

Lead  matte  for  silver,  45 
Lead  ores,  190 

classification,  191 
Lead  silicates,  69 

and  iron,  69,  192,  196 
and  sulphides,  102 
Lead  speiss,  assay  for  silver,  45 
Lead  sulphide  and  iron,  6,  74,  192 
Limestone,  assay  for  gold,  129 
silver,  89 
Litharge,  6,  7,  68,  80 

action  on  metals,  69 

sulphides,  69 
amount  absorbed  by  cupel, 

59 
amount  to  use  with  sulphide 

ores,  104,  105 
and  carbon,  6,  70,  84 
and  iron,  6,  70,  74 
and  nitre  fusion,  103,  139, 

142 


INDEX. 


3°9 


Litharge  and    nitre    fusion,    ad  van - 
•    tages  and  disadvantages, 

142 

and  sulphides,  7,  69,  70 
assay  for  silver,  80 
ratio  to  copper  in  ore,  121 
silica,  and  soda,  69 
testing  for  silver  and  gold, 

80 

Litharge  crystals,  56,  65 
Loss  of  gold  in  cupelling,  160 
scorifying,  128 
silver  in  cupelling,  62 
scorifying,  65 
Lutes,  23 

Magnesia,  best  flux  for,  75 
Manganese  binoxide,  6,  72 

influence  on 
size  of  lead 
button,  93 

Manganiferous  ores,  45 
Matte,  10,  n 

assay  of,  49,  180 
iron,  112 
Mercury,  cleaning  of,  292 

recovery  from  solutions,  286 
retorting  of,  290 

Metallic  copper,  assay  for  silver,  53 
Metallic  particles,  30,  31,  32,  33,  34 
Metallic    particles    forcing    through 

sieve,  30 

Metallurgical  laboratory: 
experiments  and  notes,  243 
general  directions,  243 
Mixing  the  sample,  31,  40,  164 
Mortars,  23 
Muffle  chloridizing  roast,  293 

report    on, 

299 
Muffle  fusion,  92,  115,  130,  131,  142, 

i93>  J94 
effect  of  temperature, 

86,  93>  "S 
Muffles,  22 

care  of,  23 
life  of,  23 
repairing,  24 
setting,  23 
size,  22 

Nickel  ores  for  silver,  45 
in  cupellation,  57 


Nickel  speiss,  10 

Nitre,  7,  8,  72,  81 
and  lead,  68 
and  litharge  fusion,  103,  139, 

142 

and  size  of  lead  button,  79 
and  sulphides,  7,  72,  81,  103 
incorrect  oxidizing  power  of,  82 
influence  on  silver  results,  104 
oxidizing  power,  81,  82 

Nitric  acid,  strength  in  parting,  152 

Organic  matter  in  ores,  116 
Osmium,  224,  227,  240 
Oxide  of  iron,  6,  72 

influence    on    size    of 

lead  button,  73 
Oxide  ores: 

crucible  assay  for  silver,  88 
crucible  assay  for  gold,  129,  130 
Oxidizing  agents,  6 

definition,  7 

Oxidizing  power  of  nitre,  81,  82 
ores,  72 

incorrect 

value,  82 
Oxygen,  6,  7 

Palladium,  224,  227,  240 
Pan  amalgamation,  300 

reactions,  301 
report  on,  302 
Panning  test,  35 
Parting  silver  and  gold,  151 
Parting  with  H2SO4,  162 
Parting,  acids  to  use,  151 

transferring  the  gold,  155 
Pellets,  calculation,  32 

examples,  33,  34,  35>  36,  37 
Peroxides  in  slag,  92 
Platinum,  224,  239 

and  H2SO4,  163,  231 
effect  of  gold  on  parting, 

236,  237 
effect  of  silver  on  parting, 

232,  237 

qualitative  tests,  225 
quantitative  analysis,  228 
separation  from  gold,  157, 

23 1 
from  silver  and 

gold,  231 
and  silver  alloys,  235 


3io 


INDEX. 


Platinum,  sources  of,  224 

table  of  solubility,  226 
Platinum  bullion,  229,  232 
Platinum  group,  table  of  solubility, 

226 

Platinum  ores,  assay  of,  228 
Plattner  chlorination,  245 

report,  249 

Poisoning  by  KCN,  269 
Potassium  carbonate,  66 
Potassium  cyanide,  6,  270 

poisoning  by,  269 
titration  of  solu- 
tion, 271 
Potassium  nitrate,  7,  8,  72,  81 

and  metallic  lead, 

72 
and  sulphides,   7, 

72,81 
Preliminary  fusion,  94 

effect  of  silica,  96 
borax,  96 
soda,  97, 
98,  99 
tempera- 
ture, 
101 
Pyrrhotite,  assay  of,  123 

Quartation,  152 
Quartering,  28,  29 

Reactions  in  scorification,  43 
Reagents,  5,  66 

testing  of,  79 
Recovery  of  mercury  from  solutions, 

286  ' 

silver  from  solutions,  209 
Reducing  agents,  5,  83 

definition,  5 

Reducing  power,  determination  of,  83 
influence  of  silica, 

84 

influence  of   differ- 
ent reagents,  120 
of  ores,  94 

true,  94 
working,  94 
true  value,  81 

Refining  flux  for  copper,  217 
Refractories,  12 
Regulus,  10 
Repairing  furnaces,  24 


Repairing  muffles,  24 
Rescorifying  buttons,  46 
Results,  closeness  of,  in  ores,  156 

reporting,  58 
Retorting  mercury,  290 
Rhodium,  224,  227,  233 
Roast,  chloridizing,  245 
dead,  133,  214 
sulphatizing,  245 
Roasted  ore,  assay  for  gold,  129 

treatment  by  bromine 

272 
Roasting,  244,  246 

an  ore,  131,  157 

reactions,  133,  215: 
Roasting  and  reaction  process,  245 
Rolling  the  sample,  31,  40 
Ruthenium,  224,  227,  242 
oxides,  242 

Salt,  73 

Sample,  final  one,  30 

fineness  of,  26,  30,  164 
labelling,  25 

mixing  and  rolling,  30,  40 
Sampling,  25 

methods,  27 
Cornish  method,  28 
necessity  of  cleaning  ma- 
chines, 26,  32 
Scorification,  reactions,  43 
Scorification  method: 
for  gold  ores,  128,  131 
for  silver  ores,  39 
fusion  period,  41 
liquefaction  period,  42 
roasting  period,  41 
scorification  period,  41 
Scorifiers,  19 

addition  of  SiO2  to,  20 
color  after  using,  46 
effect  of  diameter  on  size 

of  lead  button,  46 
size,  19 
Silica,  73,  84,  85 

addition  to  a  fusion,  106 
and  litharge,  69 
influence     on     the     reducing 
power  of  a  substance,  84,, 
.   85,9.6 

in  scorification,  44 
safe  ratio  to  soda,  108 
soda,  and  litharge,  69 


INDEX. 


Silicates  of  soda,  67 
Silicious  ore: 

assay  for  gold,  129,  130 
assay  for  silver,  88,  92 
Silver,  assay  of  solutions,  183 

combination     wet     and     dry 

method,  54 
effect  of   increasing  ratio   to 

gold  on  gold  loss,  162 
experiment  with  C.P.,  59 
fusing-point,  39 
in  bismuth,  183 

star  antimony,  182 
recovery  from  solutions,  209, 

286 

Silver  amalgam,  284,  285 
Silver   and    copper   alloys,    cupella- 

tion  of,  204 
Silver  bead,  weighing  of,  58 

of  unusual  appearance, 

65 

Silver  bullion,  198,  201,  205 
Silver  button,  blicking,  56,  61 

cleaning,  58 
Silver  chloridizing  roast,  293 

re  port  on,  299 

Silver  loss  due  to  nitre,  114 
Silver  losses  in  cupelling,  58,  59,  61, 

65 

influence  of  bone-ash,  61 
cupel,  61 
copper,  64,  65 
lead,  64 
tellurium,  65 
temperature,  62 
Silver  ores,  assay  of,  39 

crucible  method,  66 
pan  amalgamation,  300 
scorification  method,  39 
with    small    amount    of 

sulphides,  106 
Size  of  lead  buttons,  116 
Slag,  9,  10 

.    assay  of,  170,  177,  195 

effect  of  temperature  on  color, 

10 

Soda,  litharge,  and  silica,  69 
Sodium  carbonate,  66 

and   metallic   sul- 
phides,   67,    98 
influence    on    re- 
ducing    power, 
84,  97 


Sodium  nitrate,  7,  72 
Sodium  silicates,  67 
Solutions,  assay  of,  183 

making  up  of,  243 
Spatula,  for  taking  samples,  30 
Special  methods,  1 18 

gold  in  zinc-box  residues,  163 
silver  in  antimonial  ores,  122 

copper  ores,  118 
Speiss,  10,  ii 

influence   of  temperature  on. 

formation,  137 
iron,  10 
lead,  45 
nickel,  10 

Sperrylite,  225,  228 
Spitting  of  ores,  48 
Split  shovel,  29 
Sprouting  of  button,  56,  57 
Stamp-mill  work,  283 
Stanniferous  ores,  assay  for  silver,  45; 
Starch,  6,  71 
Sterling  silver,  5 
Sulphates,    action    in    presence    of 

litharge,  78 

Sulphates,  decomposition  by  heat,  135: 
order  of  decomposition  by 

heat,  294 

roasted-ore  test,  268 
Sulphatizing  roast,  245 
Sulphides  and  lead  silicates,  102 

bicarb,  soda,  67,  98 
Sulphide  ores,  assay  for  silver,  103,. 
106,     i  10, 

III,     112 

gold,       131^ 

i33>  J39 
Sulphur,  8 

Sulphuric  acid,  parting  with,  162 
Sulphurizing  agents,  8 
Surcharge,  162 

Telluride  ores,  assay  of,  143 
Tellurium,  effect  on  gold  in  cupella- 

tion,  150 
test  for,  149 

Temperature,  effect  of  insufficient,  in 
muffle  fusion,  86,  93, 

"5 
influence  on   color  of 

slag,  9.  10 
influence    on    cupella- 

tion  of  gold,  1 60 


312 


INDEX 


Temperature,  influence    on    cupella- 

tion  of  silver,  62 
influence  on   the   for- 
mation of  speiss,  137 
influence   on"  size    of 
lead  button,  86, 101, 
116 
Testing  a  roasted  ore  for  sulphates, 

268 
Testing-reagents,  79 

R.P.  of  reagents,  83 
Time  of  fusion,  90,  94,  108,  136,  193, 

215,  222 
Tin,  219 

effect  of  SiO2  on  fusion,  220 
methods  of  assay,  221,  222 
steps  in  assay,  220 
Tin  ores,  219 
Tongs,  annealing-cup,  155 
crucible,  14 
cupel,  14 
lead  assay,  193 
scorifier,  14,  41 
True  R.P.  of  an  ore,  81,  94 

Van  Liew's  wet  method  for  gold,  181 
silver,  54 


Vanning  shovel,  87,  133,  281 
Vanning  test,  35 

for  character  of  ore,  134 
Vapors,  color  from  scorification,  41 
Volhard's  wet  method  for  bullion,  207 
Volumetric  method  for  silver,  199,  207 


Washing  test  for  character  of  ore,  134 
Weighing  silver  beads,  58 

and  gold  beads,  150 
Weights,  2 

memoranda,  4 
White  flux,  194 
Working  R.P.  of  an  ore,  81,  94 

Zinc  blende,  assay  of,  45,  108 
Zinc  sulphate,  78 

Zinc-box  residues,  assay  for  gold,  163 
silver,  163 
best     charge     for 
scorification,  1 7 1, 
.       180 

Zinc,  reactions  in  cupellation,  59 
scorification,  44 


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Landauer's  Spectrum  Analysis.     (Tingle.) 8vo,  3  oo 

*  Langworthy  and  Austen.        The  Occurrence  of  Aluminium  in  Vegetable 

Products,  Animal  Products,  and  Natural  Waters 8vo,  2  oo 

Lassar-Cohn's  Practical  Urinary  Analysis.  (Lorenz.) i2mo,  i  oo 

Application  of  Some  General  Reactions  to  Investigations  in  Organic 

Chemistry.  (Tingle.) i2mo,  i  oo 

Leach's  The  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

Control 8vo,  7  50 

Lob's  Electrochemistry  of  Organic  Compounds.  (Lorenz.) 8vo,  3  oo 

Lodge's  Notes  on  Assaying  and  Metallurgical  Laboratory  Experiments 8vo,  3  oo 

Low's  Technical  Method  of  Ore  Analysis 8vo,  3  oo 

Lunge's  Techno-chemical  Analysis.  (Cohn.) i2mo  i  oo 

*  McKay  and  Larsen's  Principles  and  Practice  of  Butter-making" 8vo,  i  50 

Mandel's  Handbook  for  Bio-chemical  Laboratory i2mo,  i  50 

*  Martin's  Laboratory  Guide  to  Qualitative  Analysis  with  the  Blowpipe .  .  i2mo,  60 
Mason's  Water-supply.     (Considered  Principally  from  a  Sanitary  Standpoint.) 

3d  Edition,  Rewritten , 8vo,  4  oo 

Examination  of  Water.     (Chemical  and  Bacteriological.) 12010,  i  25 

Matthew's  The  Textile  Fibres 8vo,  3  50 

Meyer's  Determination  of  Radicles  in  Carbon  Compounds.     (Tingle.).  .i2mo,  i  oo 

Miller's  Manual  of  Assaying i2mo,  i  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.) ....  i2mo,  2  50 

Mixter's  Elementary  Text-book  of  Chemistry.  . I2mo,  i  50 

4 


Morgan's  An  Outline  of  the  Theory  of  Solutions  and  its  Results i2tno,  i  oo 

Elements  of  Physical  Chemistry izmo,  3  oo 

*  Physical  Chemistry  for  Electrical  Engineers I2mo,  i  50 

Morse's  Calculations  used  in  Cane-sugar  Factories i6mo,  morocco,  i  50 

Mulliken's  General  Method  for  the  Identification  of  Pure  Organic  Compounds. 

Vol.  I Large  8vo,  5  oo 

O'Brine's  Laboratory  Guide  in  Chemical  Analysis 8vo,  2  oo 

O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  oo 

Ostwald's  Conversations  on  Chemistry.     Part  One.     (Ramsey.) i2mo,  i  50 

"               "           "             Part  Two.     (Turnbull.) i2mo,  200 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of  Mineral  Tests. 

8vo,  paper,  50 

Pictet's  The  Alkaloids  and  their  Chemical  Constitution.     (Biddle.) 8vo,  5  oo 

Pinner's  Introduction  to  Organic  Chemistry.     (Austen.) I2mo,  i  50 

Poole's  Calorific  Power  of  Fuels 8vo,  3  oo 

Prescott  and  Winslow's  Elements  of  Water  bacteriology,  with  Special  Refer- 
ence to  Sanitary  Water  Analysis i2mo,  i  25 

*  Reisig's  Guide  to  Piece-dyeing 8vo,  25  oo 

Richards  and  Woodman's  Air.Water,  and  Food  from  a  Sanitary  Standpoint.  ,8vo,  2  oo 
Ricketts  and  Russell's  Skeleton  Notes  upon  Inorganic   Chemistry.     (Part  I. 

Non-metallic  Elements.) 8vo,  morocco,  75 

Ricketts  and  Miller's  Notes  on  Assaying 8vo,  3  oo 

Rideal's  Sewage  and  the  Bacterial  Purification  of  Sewage 8vo,  3  50 

Disinfection  and  the  Preservation  of  Food 8vo,  4  oo 

Riggs's  Elementary  Manual  for  the  Chemical  Laboratory 8vo,  i  25 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

Rostoski's  Serum  Diagnosis.     (Bolduan.) I2mo,  i  oo 

Ruddiman's  Incompatibilities  in  Prescriptions 8vo,  2  oo 

*  Whys  in  Pharmacy i2mo,  i  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  60 

Salkowski's  Physiological  and  Pathological  Chemistry.     (Orndorff.) 8vo,  2  50 

Schimpf 's  Text-book  of  Volumetric  Analysis i2mo,  2  50 

Essentials  of  Volumetric  Analysis i2mo,  i  25 

*  Qualitative  Chemical  Analysis 8vo,  i   25 

Smith's  Lecture  Notes  on  Chemistry  for  Dental  Students 8vo,  2  50 

Spencer's  Handbook  for  Chemists  of  Beet-sugar  Houses i6mo,  morocco.  3  oo 

Handbook  for  Cane  Sugar  Manufacturers i6mo,  morocco,  3  oo 

Stockbridge's  Rocks  and  Soils.    • 8vo,  2  50 

*  Tillman's  Elementary  Lessons  in  Heat 8vo,  i  50 

*  Descriptive  General  Chemistry.     , 8vo,  3  oo 

Treadwell's  Qualitative  Analysis.     (Hall.) 8vo,  3  oo 

Quantitative  Analysis.     (Hall.) 8vo,  4  oo 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Van  Deventer's  Physical  Chemistry  for  Beginners.     (Boltwood.) i2mo,  i  50 

*  Walke's  Lectures  on  Explosives 8vo,  4  oo 

Ware's  Beet-sugar  Manufacture  and  Refining Small  8vo,  cloth,  4  oo 

Washington's  Manual  of  the  Chemical  Analysis  of  Rocks 8vo,  2  oo 

Wassermann's  Immune  Sera :  Haemolysins,  Cytotoxins,  and  Precipitins.    (Bol- 
duan.)   i2mo,  i  oo 

Wehrenfennig's  Analysis  and  Softening  of  Boiler  Feed-Water 8vo,  4  oo 

Wells's  Laboratory  Guide  in  Qualitative  Chemical  Analysis 8vo,  i  50 

Short  Course  in  Inorganic  Qualitative  Chemical  Analysis  for  Engineering 

Students i2mo,  i  50 

Text-book  of  Chemical  Arithmetic 1 21110,  i  25 

Whipple's  Microscopy  of  Drinking-water 8vo,  3  50 

Wilson's  Cyanide  Processes I2mo,  i  50 

Chlorination  Process I2mo,  i  50 

Winton's  Microscopy  of  Vegetable  Foods 8vo,  7  50 

Wulling's    Elementary    Course    in  Inorganic,  Pharmaceutical,  and  Medical 

Chemistry - I2mo,  a  oo 

5 


CIVIL  ENGINEERING. 

BRIDGES    AND    ROOFS.       HYDRAULICS.       MATERIALS   OF   ENGINEERING. 
RAILWAY  ENGINEERING. 

Baker's  Engineers'  Surveying  Instruments. ....  12010,  3  oo 

Bixby's  Graphical  Computing  Table Paper  19}  X  24$  inches.  25 

**  Burr's  Ancient  and  Modern  Engineering  and  the  Isthmian  Cana ..     (Postage, 

27  cents  additional.) 8vo,  3  50 

•Comstock's  Field  Astronomy  for  Engineers 8vo,  2  50 

Davis's  Elevation  and  Stadia  Tables 8vo,  I  oo 

.Elliott's  Engineering  for  Land  Drainage . i2mo,  i  50 

Practical  Farm  Drainage i2mo,  i  oo 

*Fiebeger's  Treatise  on  Civil  Engineering 8vo,  5  oo 

Flemer's  Phototopographic  Methods  and  Instruments 8vo,  5  oo 

Jolwell's  Sewerage.     (Designing  and  Maintenance.) 8vo,  3  oo 

Freitag's  Architectural  Engineering.     2d  Edition,  Rewritten 8vo,  3  50 

French  and  Ives's  Stereotomy 8vo,  2  50 

Goodhue's  Municipal  Improvements I2mo,  i  75 

Goodrich's  Economic  Disposal  of  Towns'  Refuse 8vo,  3  50 

Gore's  Elements  of  Geodesy 8vo,  2  50 

Hayford's  Text-book  of  Geodetic  Astronomy 8vo,  3  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  morocco,  2  50 

flowe's  Retaining  Walls  for  Earth i2mo,  i  25 

*  Ives's  Adjustments  of  the  Engineer's  Transit  and  Level i6mo,  Bds.  25 

Johnson's  (J.  B.)  Theory  and  Practice  of  Surveying.  ..  .- Small  8vo,  4  oo 

Johnson's  (L.  J.)  Statics  by  Algebraic  and  Graphic  Methods 8vo,  2  oo 

Laplace's  Philosophical  Essay  on  Probabilities.    (Truscott  and  Emory.) .  12010,  2  oo 

Mahan's  Treatise  on  Civil  Engineering.     (1873.)     (Wood.) 8vo,  5  oo 

*  Descriptive  Geometry 8vo  50 

Merriman's  Elements  of  Precise  Surveying  and  Geodesy 8vo,  50 

Merriman  and  Brooks's  Handbook  for  Surveyors i6mo,  morocco,  oo 

Nugent's  Plane  Surveying 8vo,  50 

•Ogden's  Sewer  Design i2mo,  oo 

Parsons's  Disposal  of  Municipal  Refuse 8ve,  oo 

Patton's  Treatise  on  Civil  Engineering 8vo  half  leather,  7  50 

Reed's  Topographical  Drawing  and  Sketching 4to,  5  oo 

Rideal's  Sewage  and  the  Bacterial  Purification  of  Sewage 8vo,  3  50 

Siebert  and  Biggin's  Modern  Stone-cutting  and  Masonry 8vo,  i  50 

Smith's  Manual  of  Topographical  Drawing.     (McMillan.) 8vo,  2  50 

-Sondericker's  Graphic  Statics,  with  Applications  to  Trusses,  Beams,  and  Arches. 

8vo,  2  oo 

Taylor  and  Thompson's  Treatise  on  Concrete,  Plain  and  Reinforced 8vo,  5  oo 

*  Trautwine's  Civil  Engineer's  Pocket-book i6mo,  morocco,  5  oo 

Venable's  Garbage  Crematories  in  America 8vo,  2  oo 

'Wait's  Engineering  and  Architectural  Jurisprudence 8vo,  6  oo 

Sheep,  6  50 

Law  of  Operations  Preliminary  to  Construction  in  Engineering  and  Archi- 
tecture  8vo,  5  oo 

Sheep,  5  50 

Law  of  Contracts 8vo,  3  oo 

^Warren's  Stereotomy — Problems  in  Stone-cutting 8vo,  2  50 

Webb's  Problems  in  the  Use  and  Adjustment  of  Engineering  Instruments. 

i6mo,  morocco,  i  25 

Wilson's  Topographic  Surveying. 8vo,  3  50 

BRIDGES  AND  ROOFS. 

Boller'c.  Practical  Treatise  on  the  Construction  of  Iron  Highway  Bridges.  .8vo,  2  oo 

"*      Thames  River  Bridge 4to,  paper,  5  oo 

6 


Burr's  Course  on  the  Stresses  in  Bridges  and  Roof  Trusses,  Arched  Ribs,  and 

Suspension  Bridges .. . . . 8vo,  3  50 

Burr  and  Falk's  Influence  Lines  for  Bridge  and  Roof  Computations.  . .  .8vo,  3  oo 

Design  and  Construction  of  Metallic  Bridges 8vo,  5  oo 

Du  Bois's  Mechanics  of  Engineering.     Vol.  II Small  4to,  10  oo 

Foster's  Treatise  on  Wboden  Trestle  Bridges 4to,  5  oo 

Fowler's  Ordinary  Foundations 8vo,  3  50 

Greene's  Roof  Trusses 8vo,  i  25 

Bridge  Trusses 8vo,  2  50 

Arches  in  Wood,  Iron,  and  Stone 8vo,  2  50 

Howe's  Treatise  on  Arches 8vo,  4  oo 

Design  of  Simple  Roof- trusses  in  Wood  and  Steel 8vo,  2  oo 

Johnson,  Bryan,  and  Turneaure's  Theory  and  Practice  in  the  Designing  of 

Modern  Framed  Structures Small  4to,  10  oo 

Merriman  and  Jacoby's  Text-book  on  Roofs  and  Bridges : 

Part  I.     Stresses  in  Simple  Trusses 8vo,  2  50 

Part  II.     Graphic  Statics 8vo,  2  50 

Part  III.     Bridge  Design 8vo,  2  50 

Part  IV.     Higher  Structures 8vo,  2  50 

Morison's  Memphis  Bridge 4to,  10  oo 

Waddeli's  De  Pontibus,  a  Pocket-book  for  Bridge  Engineers.  .  i6mo,  morocco,  2  oo 

*  Specifications  for  Steel  Bridges i2mo,  50 

Wright's  Designing  of  Draw-spans.     Two  parts  in  one  volume 8vo,  3  50 


HYDRAULICS. 

Bazin's  Experiments  upon  the  Contraction  of  the  Liquid  Vein  Issuing  from 

an  Orifice.     (Trautwine.) 8vo,  2  oo 

Bovey's  Treatise  on  Hydraulics 8vo,  5  oo 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

Diagrams  of  Mean  Velocity  of  Water  in  Open  Channels paper,  i  50 

Hydraulic  Motors 8vo,  2  oo 

Coffin's  Graphical  Solution  of  Hydraulic  Problems i6mo,  morocco,  2  50 

Flather's  Dynamometers,  and  the  Measurement  of  Power i2mo,  3  oo 

Folwell's  Water-supply  Engineering 8vo,  4  oo 

Frizell's  Water-power 8vo,  5  oo 

Fuertes's  Water  and  Public  Health i2mo,  i  50 

Water-filtration  Works i2mo,  2  50. 

Ganguillet  and  Kutter's  General  Formula  for  the  Uniform  Flow  of  Water  in 

Rivers  and  Other  Channels.     (Hering  and  Trautwine.) 8vo,  4  oo 

Hazen's  Filtration  of  Public  Water-supply 8vo,  3  oo 

Hazlehurst's  Towers  and  Tanks  for  Water-works 8vo,  2  50. 

Herschel's  115  Experiments  on  the  Carrying  Capacity  of  Large,  Riveted,  Metal 

Conduits 8vo,  2  oo 

Mason's  Water-supply.     (Considered  Principally  from  a  Sanitary  Standpoint.) 

8vo,  4  oo 

Merriman's  Treatise  on  Hydraulics 8vo,  5  oo 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,  4  oa 

Schuyler's   Reservoirs   for   Irrigation,   Water-power,   and   Domestic   Water- 
supply Large  8vo,  5  oo 

**  Thomas  and  Watt's  Improvement  of  Rivers.     (Post.,  440.  additional. ).4to,  6  oo 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oa 

Wegmann's  Design  and  Construction  of  Dams 4to,  5  oo 

Water-supply  of  the  City  of  New  York  from  1658  to  1895 410,  10  oo 

Williams  and  Hazen's  Hydraulic  Tables 8vo,  i  50 

Wilson's  Irrigation  Engineering Small  8vo,  4  oo 

Wolff's  Windmill  as  a  Prime  Mover. 8vo,  3  oo 

Wood's  Turbines 8vo,  2  50 

Elements  of  Analytical  Mechanics 8vo,  3  oo 

7 


MATERIALS  OF  ENGINEERING. 

Baker's  Treatise  on  Masonry  Construction 8vo,  5  oo 

Roads  and  Pavements 8vo,  5  oo 

Black's  United  States  Public  Works  .  . . ." Oblong  4to,  5  oo 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  the  Materials  of  Engineering 8vo,  7  50 

Byrne's  Highway  Construction 8vo,  5  oo 

Inspection  of  the  Materials  and  Workmanship  Employed  in  Construction. 

i6mo,  3  oo 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

Du  Bois's  Mechanics  of  Engineering.     Vol.  I Small  4to,  7  50 

*EckeI's  Cements,  Limes,  and  Plasters 8vo,  6  oo 

Johnson's  Materials  of  Construction Large  8vo,  6  oo 

Fowler's  Ordinary  Foundations 8vo,  3  50 

•*  Greene's  Structural  Mechanics 8vo,  2  50 

-Keep's  Cast  Iron 8vo,  2  50 

Lanza's  Applied  Mechanics 8vo,  7  50 

Marten's  Handbook  on  Testing  Materials.     (Henning.)     2  vols 8vo,  7  50 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merrill's  Stones  for  Building  and  Decoration 8vo,  5  oo 

Merriman's  Mechanics  of  Materials '. 8vo,  5  oo 

Strength  of  Materials i2mo,  i  oo 

Metcalf's  Steel.     A  Manual  for  Steel-users i2mo,  2  oo 

Patton's  Practical  Treatise  on  Foundations 8vo,  5  oo 

Richardson's  Modern  Asphalt  Pavements 8vo,  3  oo 

Richey's  Handbook  for  Superintendents  of  Construction i6mo,  mor.,  4  oo 

Rockwell's  Roads  and  Pavements  in  France i2mo,  i  25 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish... 8vo,  3  oo 

Smith's  Materials  of  Machines I2mo,  i  oo 

Snow's  Principal  Species  of  Wood 8vo,  3  50 

Spalding's  Hydraulic  Cement i2mo,  2  oo 

Text-book  on  Roads  and  Pavements i2mo,  2  oo 

Taylor  and  Thompson's  Treatise  on  Concrete,  Plain  and  Reinforced. ....  .8vo,  5  oo 

Thurston's  Materials  of  Engineering.     3  Parts 8vo,  8  oo 

Part  I.     Non-metallic  Materials  of  Engineering  and  Metallurgy 8vo,  2  oo 

Part  II.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Thurston's  Text-book  of  the  Materials  of  Construction 8vo,  5  oo 

Tillson's  Street  Pavements  and  Paving  Materials 8vo,  4  oo 

Waddell's  De  Pontibus.    (A  Pocket-book  for  Bridge  Engineers.).  .i6mo,  mer.,  2  oo 

Specifications  for  Steel  Bridges i2mo,  i  25 

"Wood's  (De  V.)  Treatise  on  the  Resistance  of  Materials,  and  an  Appendif  on 

the  Preservation  of  Timber 8vo,  2  oo 

Wood's  (De  V.)  Elements  of  Analytical  Mechanics 8vo,  3  oo 

Wood's  (M.  P.)  Rustless  Coatings:    Corrosion  and  Electrolysis  of  Iron  and 

Steel 8vo,  4  oo 


RAILWAY  ENGINEERING. 

\ 

Andrew's  Handbook  for  Street  Railway  Engineers 3x5  inches,  morocco,  i  25 

Berg's  Buildings  and  Structures  of  American  Railroads 4to,  5  oo 

Brook's  Handbook  of  Street  Railroad  Location i6mo,  morocco,  i  50 

Butt's  Civil  Engineer's  Field-book i6mo,  morocco,  2  50 

Crandall's  Transition  Curve i6mo,  morocco,  i  50 

Railway  and  Other  Earthwork  Tables.  .  .  . '. 8vo,  i  50 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book.  .  i6mo,  moroccOj  5  oo 

8 


Dredge's  History  of  the  Pennsylvania  Railroad:    (1879) Paper,  5  oo 

*  Drinker's  Tunnelling,  Explosive  Compounds,  and  Rock  Drills. 4to,  half  mor.,  25  oo 

Fisher's  Table  of  Cubic  Yards Cardboard,  25 

Godwin's  Raikoad  Engineers'  Field-book  and  Explorers'  Guide.  .  .  i6mo,  mor.,  2  50 

Howard's  Transition  Curve  Field-book i6mo,  morocco,  i  50 

Hudson's  Tables  for  Calculating  the  Cubic  Contents  of  Excavations  and  Em- 
bankments  Svo,  i  oo 

Molitor  and  Beard's  Manual  for  Resident  Engineers i6mo,  i  oo 

Nagle's  Field  Manual  for  Railroad  Engineers i6mo,  morocco,  3  oo 

Philbrick's  Field  Manual  for  Engineers i6mo,  morocco,  3  oo 

Searles's  Field  Engineering i6mo,  morocco,  3  oo 

Railroad  Spiral i6mo,  merecco,  i  50 

Taylor's  Prismoidal  Formulae  and  Earthwork 8vo,  I  50 

*  Trautwine's  Method  of  Calculating  the  Cube  Contents  of  Excavations  and 

Embankments  by  the  Aid  of  Diagrams 8vo,  2  oo 

The  Field  Practice  of  Laying  Out  Circular  Curves  for  Railroads. 

I2mo,  morocco,  2  50 

Cross-section  Sheet Paper,  25 

Webb's  Railroad  Construction i6mo,  morocco,  5  oo 

Wellington's  Economic  Theory  of  the  Location  of  Railways Small  8vo,  5  oo 


DRAWING. 

Barr's  Kinematics  of  Machinery 8vo,  2  50 

*  Bartlett's  Mechanical  Drawing .  .8vo,  3  oo 

*  "  "  "        Abridged  Ed 8vo,  150 

Coolidge's  Manual  of  Drawing 8vo,  paper  i  oo 

Coolidge  and  Freeman's  Elements  of  General  Drafting  for  Mechanical  Engi- 
neers  Oblong  4to,  2  50 

Durley's  Kinematics  of  Machines 8vo,  4  oo 

Emch's  Introduction  to  Projective  Geometry  and  its  Applications 8vo,  2  50 

Hill's  Text-book  on  Shades  and  Shadows,  and  Perspective 8vo,  2  oo 

Jamison's  Elements  of  Mechanical  Drawing 8vo,  2  50 

Advanced  Mechanical  Drawing 8vo,  2  oo 

Jones's  Machine  Design: 

Part  I.     Kinematics  of  Machinery 8vo,  i  50 

Part  II.     Form,  Strength,  and  Proportions  of  Parts 8vo,  3  oo 

MacCord's  Elements  of  Descriptive  Geometry 8vo,  3  oo 

Kinematics;  or,  Practical  Mechanism 8vo,  5  oo 

Mechanical  Drawing 4to,  4  oo 

Veloeity  Diagrams 8vo,  i  50 

MacLeod's  Descriptive  Geometry Small  8vo,  i  50 

*  Mahan's  Descriptive  Geometry  and  Stone-cutting 8vo,  i  50 

Industrial  Drawing.     (Thompson.) 8vo,  3  50 

Moyer's  Descriptive  Geometry 8vo,  2  oo 

Reed's  Topographical  Drawing  and  Sketching 4to,  5  oo 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  oo 

Smith's  (R.  S.)  Manual  of  Topographical  Drawing.     (McMillan.) 8vo,  2  50 

Smith  (A.  W.)  and  Marx's  Machine  Design 8vo,  3  oo 

Warren's  Elements  of  Plane  and  Solid  Free-hand  Geometrical  Drawing.  12 mo, 


Drafting  Instruments  and  Operations i2mo, 

Manual  of  Elementary  Projection  Drawing 12010, 

Manual  of  Elementary  Problems  in  the  Linear  Perspective  of  Form  and 

Shadow I2mo, 

Plane  Problems  in  Elementary  Geometry i2mo, 

9 


Warren's  Primary  Geometry i2mo,  75 

Elements  of  Descriptive  Geometry,  Shadows,  and  Perspective 8vo,  3  50 

General  Problems  of  Shades  and  Shadows i 8vo,  3  oo 

Elements  of  Machine  Construction  and  Drawing 8vo,  7  50 

Problems,  Theorems,  and  Examples  in  Descriptive  Geometry 8vo,  2  50 

Weisbach's    Kinematics    and    Power    of    Transmission.        (Hermann    and 

Klein.) 8vo,  5  oo 

Whelpley's  Practical  Instruction  in  the  Art  of  Letter  Engraving 12 mo,'  2  oo 

Wilson's  (H.  M.)  Topographic  Surveying 8vo,  3  50 

Wilson's  (V.  T.)  Free-hand  Perspective 8vo,  2  50 

Wilson's  (V.  T.)  Free-hand  Lettering 8vo,  i  oa 

Woolf's  Elementary  Course  in  Descriptive  Geometry Large  8vo,  3  oo 

ELECTRICITY  AND  PHYSICS. 

Anthony  and  Brackett's  Text-book  of  Physics.     (Magie.) Small  8vo,  3  oo 

Anthony's  Lecture-notes  on  the  Theory  of  Electrical  Measurements.  .  .  .  i2mo,  i  oo 

Benjamin's  History  of  Electricity 8vo,  3  oo 

Voltaic  Cell 8vo,  3  oo 

Classen's  Quantitative  Chemical  Analysis  by  Electrolysis.     (Boltwood.).8vo,  3  oo 

Crehore  and  Squier's  Polarizing  Photo-chronograph .  .8vo,  3  oo 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book.  i6mo,  morocco,  5  oo 
Dolezalek's    Theory   of    the    Lead   Accumulator    (Storage    Battery).      (Von 

Ende.) i2mo,  2  50 

Duhem's  Thermodynamics  and  Chemistry.     (Burgess.) 8vo,  4  oo 

Flather's  Dynamometers,  and  the  Measurement  of  Power i2mo,  3  oo 

Gilbert's  De  Magnete.     (Mottelay.) 8vo,  2  50 

Hanchett's  Alternating  Currents  Explained i2mo,  i  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  morocco,  2  50 

Holman's  Precision  of  Measurements :  .  8vo,  2  oo 

Telescopic   Mirror-scale  Method,  Adjustments,  and  Tests.  . .  .Large  8vo,  7S 

Kinzbrunner's  Testing  of  Continuous-current  Machines 8vo,  2  oo 

Landauer's  Spectrum  Analysis.     (Tingle.) 8vo,  3  oo 

Le  Chatelier's  High-temperature  Measurements.  (Boudouard — Burgess.)  i2mo,  3  oo 

Lob's  Electrochemistry  of  Organic  Compounds.     (Lorenz.) 8vo,  3  oo 

*  Lyons's  Treatise  on  Electromagnetic  Phenomena.   Vols.  I.  and  II.  8vo,  each,  6  oo 

*  Michie's  Elements  of  Wave  Motion  Relating  to  Sound  and  Light 8vo, 

Niaudet's  Elementary  Treatise  on  Electric  Batteries.     (Fishback.) i2mo, 


oo 
50 
So 
50 
5<» 
50 
50 


*  Parshall  and  Hobart's  Electric  Machine  Desigo 4to,  half  morocco,  i 

*  Rosenberg's  Electrical  Engineering.     (Haldane  Gee — Kinzbrunner.).  .  .8vo, 

Ryan,  Norris,  and  Hoxie's  Electrical  Machinery.     VoL  I '.  . .  .8vo, 

Thurston's  Stationary  Steam-engines 8vo, 

*  Tillman's  Elementary  Lessons  in  Heat 8vo, 

Tory  and  Pitcher's  Manual  of  Laboratory  Physics Small  8vo,    2  oo 

Ulke's  Modern  Electrolytic  Copper  Refining 8vo,    3  oo 

LAW. 

*  Davis's  Elements  of  Law 8vo,    2  50 

*  Treatise  on  the  Military  Law  of  United  States 8vo,    7  oo 

*  Sheep,    7  50 

Manual  for  Courts-martial i6mo,  morocco,     i  50 

Wait's  Engineering  and  Architectural  Jurisprudence 8vo,    6  oo 

Sheep,  6  50 

Law  of  Operations  Preliminary  to  Construction  in  Engineering  and  Archi- 
tecture  8vo  5  oo 

Sheep,  5  50 

Law  of  Contracts 8vo,  3  oo 

Winthrop's  Abridgment  of  Military  Law I2mo.  a  50 

10 


MANUFACTURES. 

Bernadou's  Smokeless  Powder— Nitro-cellulose  and  Theory  of  th?  Ceflulose 

Molecule 12010,  2  50 

Bolland's  Iron  Founder I2mo,  2  50 

"The  Iron  Founder,"  Supplement i2mo,  2  50 

Encyclopedia  of  Founding  and  Dictionary  of  Foundry  Terms  Used  in  the 

Practice  of  Moulding I2mo,  3  oo 

*  Eckel's  Cements,  Limes,  and  Plasters 8vo,  6  oo 

Eissler's  Modern  High  Explosives 8vo,  4  oo> 

Effront's  Enzymes  and  their  Applications.     (Prescott.) 8vo,  3  oo 

Fitzgerald's  Boston  Machinist I2mo,  i  oo 

Ford's  Boiler  Making  for  Boiler  Makers i8mo,  i  oo 

Hopkin's  Oil-chemists'  Handbook 8vo,  3  oo 

Keep's  Cast  Iron 8vo,  2  50 

Leach's  The  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

Control Large  8vo,  7  50 

*  McKay  and  Larsen's  Principles  and  Practice  of  Butter-making 8vo,  i  50 

Matthews's  The  Textile  Fibres 8vo,  3  50 

Metcalf's  Steel.     A  Manual  for  Steel-users i2mo,  2  oo 

Metcalfe's  Cost  of  Manufactures — And  the  Administration  of  Workshops.  8vo,  5  oo 

Meyer's  Modern  Locomotive  Construction 4to,  10  oo 

Morse's  Calculations  used  in  Cane-sugar  Factories i6mo,  morocco,  i  50 

*  Reisig's  Guide  to  Piece-dyeing 8vo,  25  oo 

Rice's  Concrete-block  Manufacture 8vo,  2  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Smith's  Press-working  of  Metals 8vo,  3  oo 

Spaldfng's  Hydraulic  Cement. i2mo,  2  oo 

Spencer's  Handbook  for  Chemists  of  Beet-sugar  Houses i6mo,  morocco,  3  oo 

Handbook  for  Cane  Sugar  Manufacturers i6mo,  morocco,  3  oo 

Taylor  and  Thompson's  Treatise  on  Concrete,  Plain  and  Reinforced 8vo,  5  oo 

Thurston's  Manual  of  Steam-boilers,  their  Designs,  Construction  and  Opera- 
tion  8vo,  5  oo 

*  Walke's  Lectures  on  Explosives 8vo,  4  oo 

Ware's  Beet-sugar  Manufacture  and  Refining Small  8vo,  4  oo 

West's  American  Foundry  Practice i2mo,  2  50 

Moulder's  Text-book I2mo,  2  50 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Rustless  Coatings:  Corrosion  and  Electrolysis  of  Iron  and  Steel.  .8vo,  4  oo 

MATHEMATICS. 

Baker's  Elliptic  Functions. 8vo,  I  50 

*  Bass's  Elements  of  Differential  Calculus I2mo,  4  oo 

Briggs's  Elements  of  Plane  Analytic  Geometry 121110,  oo 

Compton's  Manual  of  Logarithmic  Computations 1 2ino,  50 

Davis's  Introduction  to  the  Logic  of  Algebra.  . 8vo,  50 

*  Dickson's  College  Algebra Large  izmo,  50 

*  Introduction  to  the  Theory  of  Algebraic  Equations Large  121110,  25 

Emch's  Introduction  to  Projective  Geometry  and  its  Applications 8vo,  50 

Halsted's  Elements  of  Geometry 8vo,  75 

Elementary  Synthetic  Geometry 8vo,  50 

Rational  Geometry i2mo,  75 

*  Johnson's  (J.  B.)  Three-place  Logarithmic  Tables:  Vest-pocket  size. paper,  15 

100  copies  for  5  oo 

*  Mounted  on  heavy  cardboard,  8  X  TO  inches,  25 

10  copies  for  2  oo 

Johnson'g  (W.  W.)  Elementary  Treatise  on  Differential  Calculus.  .Small  8vo,  3  oo 

Elementary  Treatise  on  the  Integral  Calculus Small  8vo,  i  50 

11 


Johnson's  (W.  W.)  Curve  Tracing  in  Cartesian  Co-ordinates i2mo,     i  oo 

Johnson's  (W.  W.)  Treatise  on  Ordinary  and  Partial  Differential  Equations. 

Small  8vo,    3  50 
Johnson's  (W.  W.)  Theory  of  Errors  and  the  Method  of  Least  Squares.  12 mo,     i  50 

*  Johnson's  (W.  W.)  Theoretical  Mechanics lamo,    3  oo 

Laplace's  Philosophical  Essay  on  Probabilities.     (Truscott  and  Emory.) .  i2mo,    2  oo 

*  Ludlow  and  Bass.     Elements  of  Trigonometry  and  Logarithmic  and  Other 

Tables 8vo,    3  oo 

Trigonometry  and  Tables  published  separately Each,    2  oo 

*  Ludlow's  Logarithmic  and  Trigonometric  Tables 8vo,     i  oo 

Manning's  Irrational  Numbers  and  their  Representation  by  Sequences  and  Series 

i2mo,     i  25 
Mathematical  Monographs.     Edited  by  Mansfield  Merriman  and  Robert 

S.  Woodward Octavo,  each     i  oo 

No.  i.  History  of  Modern  Mathematics,  by  David  Eugene  Smith. 
No.  2.  Synthetic  Projective  Geometry,  by  George  Bruce  Halsted. 
No.  3.  Determinants,  by  Laenas  Gifford  Weld.  No.  4.  Hyper- 
bolic Functions,  by  James  McMahon.  No.  5.  Harmonic  Func- 
tions* by  William  E.  Byerly.  No.  6.  Grassmann's  Space  Analysis, 
by  Edward  W.  Hyde.  No.  7.  Probability  and  Theory  of  Errors, 
by  Robert  S.  Woodward.  No.  8.  Vector  Analysis  and  Quaternions, 
by  Alexander  Macfarlane.  No.  9. "iDifferential  Equations,  by 
"William  Woolsey  Johnson.  No.  10.  The  Solution  of  Equations, 
by  Mansfield  Merriman.  No.  n.  Functions  of  a  Complex  Variable, 
by  Thomas  S.  Fiske. 

Maurer's  Technical  Mechanics 8vo,    4  oo 

Merriman's  Method  of  Least  Squares .' 8vo,    2  oo 

Rice  and  Johnson's  Elementary  Treatise  on  the  Differential  Calculus. .  Sm.  Svo,.   3  oo 

Differential  and  Integral  Calculus.     2  vols.  in  one Small  Svo,    2  50 

Wood's  Elements  of  Co-ordinate  Geometry Svo,    2  oo 

Trigonometry;  Analytical,  Plane,  and  Spherical i2mo,    i  oo 


MECHANICAL  ENGINEERING. 

MATERIALS  OF  ENGINEERING,  STEAM-ENGINES  AND  BOILERS. 

Bacon's  Forge  P/actice i2mo,  i  50 

Baldwin's  Steam  Heating  for  Buildings i2mo,  2  50 

Barr's  Kinematics  of  Machinery .x Svo,  2  50 

*  Bartlett's  Mechanical  Drawing Svo,  3  oo 

"        Abridged  Ed Svo,  i  50 

Benjamin's  Wrinkles  and  Recipes i2mo,  2  oo 

Carpenter's  Experimental  Engineering Svo,  6  oo 

Heating  and  Ventilating  Buildings Svo,  4  oo 

Cary's  Smoke  Suppression  in  Plants  using  Bituminous  Coal.     (In  Prepara- 
tion. ) 

Clerk's  Gas  and  Oil  Engine .Small  Svo,  4  oo 

Coolidge's  Manual  of  Drawing Svo,  paper,  i  oo 

Coolidge  and  Freeman's  Elements  of  General  Drafting  for  Mechanical  En- 
gineers   Oblong  4to,  2  50 

Cromwell's  Treatise  on  Toothed  Gearing i2mo,  i  50 

Treatise  on  Belts  and  Pulleys i2mo,  i  50 

Durley's  Kinematics  of  Machines Svo,  4  oo 

Flather's  Dynamometers  and  the  Measurement  of  Power i2mo,  3  oo 

Rope  Driving i2mo,  2  oo 

Gill's  Gas  and  Fuel  Analysis  for  Engineers i2mo,  i  25 

Hall's  Car  Lubrication i2mo,  i  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  morocco,  2  50 

12 


Button's  The  Gas  Engine 8vo,  5  oo 

Jamison's  Mechanical  Drawing 8vo,  2  50 

Jones's  Machine  Design: 

Part  I.     Kinematics  of  Machinery 8vo,  i  50 

Part  II.     Form,  Strength,  and  Proportions  of  Parts 8vo,  3  oo 

Kent's  Mechanical  Engineers'  Pocket-book i6mo,  morocco,  5  oo 

Kerr's  Power  and  Power  Transmission 8vo,  2  oo 

Leonard's  Machine  Shop,  Tools,  and  Methods 8vo,  4  oo 

*  Lorenz's  Modern  Refrigerating  Machinery.    (Pope,  Haven,  and  Dean.)  .  .  8vo,  4  oo 

.MacCord's  Kinematics;   or,  Practical  Mechanism 8vo,  5  oo 

Mechanical  Drawing 4to,  4  oo 

Velocity  Diagrams 8vo,  i  50 

MacFar land's  Standard  Reduction  Factors  for  Gases 8vo,  i  50 

Mahan's  Industrial  Drawing.     (Thompson.) 8vo,  3  50 

Poole's  Calorific  Power  of  Fuels 8vo,  3  oo 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Hichard's  Compressed  Air I2mo,  i  50 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Schwamb  and  Merrill's  Elements  of  Mechanism ..." 8vo,  3  oo 

Smith's  (O.)  Press-working  of  Metals 8vo,  3  oo 

Smith  (A.  W.)  and  Marx's  Machine  Design 8vo,  3  oo 

Thurston's   Treatise    on   Friction  and   Lost   Work   in   Machinery   and   Mill 

Work 8vo,  3  oo 

Animal  as  a  Machine  and  Prime  Motor,  and  the  Laws  of  Energetics.  i2mo,  I  oo 

"Warren's  Elements  of  Machine  Construction  and  Drawing 8vo,  7  5<> 

Weisbach's    Kinematics    and    the    Power    of    Transmission.     (Herrmann — 

Klein.) 8vo,  5  oo 

Machinery  of  Transmission  and  Governors.     (Herrmann — Klein.).  .8vo,  5  oo 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Turbines 8vo,  2  50 


MATERIALS   OP   ENGINEERING. 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  the  Materials  of  Engineering.    6th  Edition. 

Reset 8vo,  7  50 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Johnson's  Materials  of  Construction 8vo,  6  oo 

Keep's  Cast  Iron 8vo,  2  50 

Lanza's  Applied  Mechanics 8vo,  7  So 

Martens 's  Handbook  on  Testing  Materials.     (Henning.) 8vo,  7  50 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merriman's  Mechanics  of  Materials.  . 8vo,  5  oo 

Strength  of  Materials 12010,  i  oo 

Metcalf's  Steel.     A  manual  for  Steel-users i2mo,  2  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  o*b 

Smith's  Materials  of  Machines ' I2mo,  i  oo 

Thurston's  Materials  of  Engineering 3  vols.,  8vo,  8  oo 

Part  II.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents. .  : 8vo,  2  50 

Text-book  of  the  Materials  of  Construction 8vo,  5  oo 

"Wood's  (De  V  )  Treatise  on  the  Resistance  of  Materials  and  an  Appendix  on 

the  Preservation  of  Timber 8vo,  2  oo 

Elements  of  Analytical  Mechanics 8vo,  3  oo 

13 


Wood's  (M.  P.)  Rustless  Coatings:    Corrosion  and  Electrolysis  of  Iron  and 

Steel 8vo,  4  oo- 

STEAM-ENGINES  AND  BOILERS. 

Berry's  Temperature-entropy  Diagram ." i2mo,  i  25 

Carnot's  Reflections  on  the  Motive  Power  of  Heat.     (Thurston.) izmo,  i  50 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book.  . . . i6mo,  mor.,  5  oo 

Ford's  Boiler  Mafcing  for  Boiler  Makers i8mo,  i  oa 

Goss's  Locomotive  Sparks 8vo,  2  oo 

Hemenway's  Indicator  Practice  and  Steam-engine  Economy i2mo,  2  oo 

Button's  Mechanical  Engineering  of  Power  Plants .8vo,  5  oo- 

Heat  and  Heat-engines 8vo.  5  oo 

Kent's  Steam  boiler  Economy 8vo,  4  oo 

Kneass's  Practice  and  Theory  of  the  Injector 8vo,  i  50- 

MacCord's  Slide-valves 8vo,  2  oa 

Meyer's  Modern  Locomotive  Construction 4to,  10  oc 

Peabody's  Manual  of  the  Steam-engine  Indicator I2mo.  i  50- 

Tables  of  the  Properties  of  Saturated  Steam  and  Other  Vapors   8vo,  i  oo- 

Thermodynamics  of  the  Steam-engine  and  Other  Heat-engines 8vo,  5  oo 

Valve-gears  for  Steam-engines '. .  .8vo,  2  50- 

Peabody  and  Miller's  Steam-boilers 8vo,  4  oo 

Fray's  Twenty  Years  with  the  Indicator Large  8vo,  2  50- 

Pupin's  Thermodynamics  of  Reversible  Cycles  in  Gases  and  Saturated  Vapors. 

(Osterberg.) i2mo,  i  25 

Reagan's  Locomotives:  Simple   Compound,  and  Electric i2mo,  2  50 

Rontgen's  Principles  of  Thermodynamics.     (Du  Bois.) 8vo,  5  oo 

Sinclair's  Locomotive  Engine  Running  and  Management .121110,  2  oo 

Smart's  Handbook  of  Engineering  Laboratory  Practice 12 mo,  2  50 

Snow's  Steam-boiler  Practice 8vo,  3  oo 

Spangler's  Valve-gears 8vo,  2  50 

Notes  on  Thermodynamics i2mo,  i  oa 

Spangler,  Greene,  and  Marshall's  Elements  of  Steam-engineering 8vo,  3  oa 

Thomas's  Steam-turbines ... 8vo,  3  50 

Thurston's  Handy  Tables 8vo,  i  50 

Manual  of  the  Steam-engine 2  vols.,  8vo,  10  oa 

Part  I.     History,  Structure,  and  Theory 8vo,  6  oa 

Part  H.     Design,  Construction,  and  Operation 8vo,  6  oo 

Handbook  of  Engine  and  Boiler  Trials,  and  the  Use  of  the  Indicator  and 

the  Prony  Brake 8vo,  5  oa 

Stationary  Steam-engines 8vo,  2  50 

Steam-boiler  Explosions  in  Theory  and  in  Practice i2mo,  i  50 

Manual  of  Steam-boilers,  their  Designs,  Construction,  and  Operation 8vo.  5  oo 

Wehrenfenning's  Analysis  and  Softening  of  Boiler  Feed-water  (Patterson)  8vo,  4  oo 

Weisbach's  Heat,  Steam,  and  Steam-engines.     (Du  Bois.) 8vo,  5  oo 

Whitham's  Steam-engine  Design 8vo,  5  oo 

Wood's  Thermodynamics,  Heat  Motors,  and  Refrigerating  Machines. .  .8vo,  4  oo 


MECHANICS  AND  MACHINERY. 

Barr's  Kinematics  of  Machinery 8vo,  2  50 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures   8vo,  7  50 

Chase's  The  Art  of  Pattern-making i2mo,  2  50 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

Notes  and  Examples  in  Mechanics 8vo,  2  oo 

Compton's  First  Lessons  in  Metal- working izmo,  i  50 

Compton  and  De  Groodt's  The  Speed  Lathe I2mo,  i  50 

14 


Cromwell's  Treatise  on  Toothed  Gearing i2mo,  i  50 

Treatise  on  Belts  and  Pulleys i2mo,  i  50 

Dana's  Text-book  of  Elementary  Mechanics  for  Colleges  and  Schools.  .  i2mo,  i  50 

.Dingey's  Machinery  Pattern  Making i2mo,  2  oo 

Dredge's  Record  of  the  Transportation  Exhibits  Building  of  the  World's 

Columbian  Exposition  of  1893 4to  half  morocco,  5  oo 

Du  Bois's  Elementary  Principles  of  Mechanics : 

Vol.      I.     Kinematics 8vo,  3  50 

Vol.    II.     Statics 8vo,  4  oo 

Mechanics  of  Engineering.     Vol.    I Small  4to,  7  50 

Vol.  II Small  4to,  10  oo 

Durley's  Kinematics  of  Machines 8vo,  4  oo 

Fitzgerald's  Boston  Machinist i6mo,  i  oo 

Flather's  Dynamometers,  and  the  Measurement  of  Power i2mo,  3  oo 

Rope  Driving 12 mo,  2  oo 

Goss's  Locomotive  Sparks STO,  2  oo 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Hall's  Car  Lubrication i2mo,  i  oo 

Holly's  Art  of  Saw  Filing '. i8mo,  75 

James's  Kinematics  of  a  Point  and  the  Rational  Mechanics  of  a  Particle. 

Small  8vo,  2  oo 

*  Johnson's  (W.  W.)  Theoretical  Mechanics i2mo,  3  oo 

Johnson's  (L.  J.)  Statics  by  Graphic  and  Algebraic  Methods 8vo,  2  oo 

Jones's  Machine  Design: 

Part    I.     Kinematics  of  Machinery 8vo,  i  50 

Part  II.     Form,  Strength,  and  Proportions  of  Parts 8vo,  3  oo 

Kerr's  Power  and  Power  Transmission 8vo  2  oo 

Lanza's  Applied  Mechanics 8vo,  7  50 

Leonard's  Machine  Shop,  Tools,  and  Methods „  .  . .  .8vo,  4  oo 

*  Lorenz's  Modern  Refrigerating  Machinery.     (Pope,  Haven,  and  Dean.). 8vo,  4  oo 
MacCord's  Kinematics;  or,  Practical  Mechanism 8vo,  5  oo 

Velocity  Diagrams 8vo,  i   50 

*  Martin's  Text  Book  on  Mechanics,  Vol.  I,  Statics I2mo,  i  25 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merriman's  Mechanics  of  Materials 8vo,  5  oo 

*  Elements  of  Mechanics i2mo,  i  oo 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,  4  oo 

*  Parshall  and  Hobart's  Electric  Machine  Design 4to,  half  morocco,  12  50 

Reagan's  Locomotives:   Simple,  Compound, 'and  Electric i2mo,  .2  50 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Richards's  Compressed  Air i2mo,  i  50 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Ryan,  No/ris,  and  Hoxie's  Electrical  Machinery.     Vol.  1 8vo,  2  50 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  oo 

Sinclair's  Locomotive-engine  Running  and  Management I2mo,  2  oo 

Smith's  (O.)  Press-working  of  Metals 8vo,  3  oo 

Smith's  (A.  W.)  Materials  of  Machines ., i2mo,  i  oo 

Smith  (A.  W.)  and  Marx's  Machine  Design 8vo,  3  oo 

Spangler,  Greene,  and  Marshall's  Elements  of  Steam-engineering 8vo,  3  oo 

Thurston's  Treatise  on  Friction   and  Lost  Work  in    Machinery  and    Mill 

Work 8vo,  3  oo 

Animal  as  a  Machine  and  Prime  Motor,  and  the  Lawc  of  Energetics.  i2mo,  i  oo 

Warren's  Elements  of  Machine  Construction  and  Drawing 8vo,  7  50 

Weisbach's  Kinematics  and  Power  of  Transmission.   (Herrmann — Klein.). 8vo,  5  oo 

Machinery  of  Transmission  and  Governors.      (Herrmann — Klein.). 8vo,  5  oo 

/             Wood's  Elements  of  Analytical  Mechanics 8vo,  3  oo 

Principles  of  Elementary  Mechanics i2mo,  i  25 

Turbines 8vo ,  2  50 

The  World's  Columbian  Exposition  of  1893 4to,  i  oo 

15  / 


METALLURGY. 

Egleston's  Metallurgy  of  Silver,  Geld,  and  Mercury: 

Vol.    I.     Silver 8vo,  7  50 

Vol.  II.     Gold  and  Mercury 8vo,  7  50 

Goesel's  Minerals  and  Metals:     A  Reference  Book , .  . .  .  i6mo,  mor.  3  oo 

**  Iles's  Lead-smelting.     (Postage  9  cents  additional.) lamo,  2  50 

Keep's  Cast  Iron 8vo,  2  50 

Kunhardt's  Practice  of  Ore  Dressing  in  Europe 8vo,  i  50 

Le  Chatelier's  High-temperature  Measurements.  (Boudouard — Burgess. )i2mo.  3  oo 

Metcalf' s  Steel.     A  Manual  for  Steel-users i2mo,  2  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.). . .  .  i2mo,  2  50 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

Smith's  Materials  of  Machines i2mo,  i  oo 

Thurston's  Materials  of  Engineering.     In  Three  Parts 8vo,  8  oo 

Part    II.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Hike's  Modern  Electrolytic  Copper  Refining 8vo,  3  oo 


MINERALOGY. 

Barringer's  Description  of  Minerals  of  Commercial  Value.    Oblong,  morocco,  2  50 

Boyd's  Resources  of  Southwest  Virginia 8vo,  3  oo 

Map  of  Southwest  Virignia Pocket-book  form.  2  oo 

Brush's  Manual  of  Determinative  Mineralogy.     (Penfield.) 8vo,  4  oo 

Chester's  Catalogue  of  Minerals 8vo,  paper,  i  oo 

Cloth,  i  25 

Dictionary  of  the  Names  of  Minerals 8vo  3  50 

Dana's  System  of  Mineralogy Large  8vo,  half  leather,  12  50 

First  Appendix  to  Dana's  New  "  System  of  Mineralogy." Large  8vo,  i  oo 

Text-book  of  Mineralogy 8vo,  4  oo 

Minerals  and  How  to  Study  Them i2mo,  i  50 

Catalogue  of  American  Localities  of  Minerals '.  .Large  8vo,  i  oo 

Manual  of  Mineralogy  and  Petrography i2mo>  2  oo 

Douglas's  Untechnical  Addresses  on  Technical  Subjects i2mo,  i  oo 

Eakle'<£  Mineral  Tables 8vo,  i  25 

Egleston's  Catalogue  of  Minerals  and  Synonyms 8vo,  2  50 

Goesel's  Minerals  and  Metals :     A  Reference  Book i6mo,  mor.  3  oo 

Groth's  Introduction  to  Chemical  Crystallography  (Marshall) i2mo,  i  25 

Hussak's  The  Determination  of  Rock-forming  Minerals.    ( Smith.). Small  8vo,  2  oo 

Merrill's  Non-metallic  Minerals:   Their  Occurrence  and  Uses 8vp,  4  oo 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of  Mineral  Test's. 

8vo,  paper,  50 
Rosenbusch's    Microscopical   Physiography    of    the    Rock-making  Minerals. 

(Iddings.) .„ 8vo,  5  oo 

*  Tillman's  Text-book  of  Important  Minerals  and  Rocks 8vo,  2  oo 


MINING. 

Beard's  Ventilation  of  Mines I2mo,  2  50 

Boyd's  Resources  of  Southwest  Virginia 8vo,  3  oo 

Map  of  Southwest  Virginia Pocket-book  form  2  oo 

Douglas's  Untechnical  Addresses  on  Technical  Subjects i2mov  i  oo 

*  Drinker's  Tunneling,  Explosive  Compounds,  and  Rock  Drills.  .4to,hf.  mor.,  25  oo 

Eissler's  Modern  High  Explosives 8vo,  tr  ->o 

Goesel's  Minerals  and  Metals :     A  Reference  Book 161110 ,  mor.  3  oo 

16 


Goodyear's  Coal-mines  of  the  Western  Coast  of  the  United  States i2ino,  2  50 

ihlseng's  Manual  of  Mining 8vo,  5  oo 

**  Iles's  Lead-smelting.     (Postage  QC.  additional.) I2mo,  2  50 

Kunhardt's  Practice  of  Ore  Dressing  in  Europe 8vo,  i  50 

O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  oo 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

*  Walke's  Lectures  on  Explosives '. 8vo,  4  oo 

Wilson's  Cyanide  Processes i2mo,  i  50 

Chlorination  Process I2mo,  i  50 

Hydraulic  and  Placer  Mining I2mo,  2  oo 

Treatise  on. Practical  and  Theoretical  Mine  Ventilation T2ma,  i  25 


SANITARY  SCIENCE. 

Bashore's  Sani+ition  of  a  Country  House 12 mo,  i  oo 

FolwelPs  Sewerage.     (Designing,  Construction,  and  Maintenance.) 8vo,  3  oo 

Water-supply  Engineering 8vo,  4  oo 

Fowler's  Sewage  Works  Analyses i2mo,  2  oo 

Fuertes's  Water  and  Public  Health i2mo,  i  50 

Water-filtration  Works I2mo,  2  50 

Gerhard's  Guide  to  Sanitary  House-inspection i6mo,  i  oo 

Goodrich's  Economic  Disposal  of  Town's  Refuse Demy  8vo,  3  50 

Hazen's  Filtration  of  Public  Water-supplies 8vo,  3  oo 

Leach's  The  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

Control , 8vo,  7  50 

Mason's  Water-supply.  (Considered  principally  from  a  Sanitary  Standpoint)  8vo,  4  oo 

Examination  of  Water.     (Chemical  and  Bacteriological.) 12 mo,  i  25 

Ogden's  Sewer  Design I2mo,  2  oo 

Prescott  and  Winslow's  Elements  of  Water  Bacteriology,  with  Special  Refer- 
ence to  Sanitary  Water  Analysis i2mo,  i  25 

*  Price's  Handbook  on  Sanitation i2mo,  i  50 

Richards's  Cost  of  Food.     A  Study  in  Dietaries i2mo,  i  oo 

Cost  of  Living  as  Modified  by  Sanitary  Science I2mo,  i  oo 

Cost  of  Shelter i2mo,  i  oo 

Richards  and  Woodman's  Air,  Water ,a  and  Food  from  a  Sanitary  Stand- 
point  8vo,  2  oo 

*  Richards-and  Williams's  The  Dietary  Computer 8vo,  i  50 

Rideal's  Sewage  and  Bacterial  Purification  of  Sewage 8vo,  '3.  50 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Von  Behring's  Suppression  of  Tuberculosis.     (Bolduan.) I2mo,  i  oo 

Whipple's  Microscopy  of  Drinking-water 8vo,  3  50 

Winton's  Microscopy  of  Vegetable  Foods 8vo,  7  50 

Woodhull's  Notes  on  Military  Hygiene. i6mo,  i  50 

*  Personal  Hygiene i2mo,  i  oo 


MISCELLANEOUS. 

De  Fursac's  Manual  of  Psychiatry.     (Rosanoff  and  Collins.).  .  .  .Large  i2mo,    2  50 

Ehrlich's  Collected  Studies  on  Immunity  ( Bolduan) 8vo,     6  oo 

Emmons's  Geological  Guide-book  of  the  Rocky  Mountain  Excursion  of  the 


International  Congress  of  Geologists Large  Cvo, 

Ferrel's  Popular  Treatise  on  the  Winds 8vo. 

Haines's  American  Railway  Management I2mo, 

Mott's  Fallacy  of  the  Present  Theory  of  Sound i6mo, 

Ricketts's  History  of  Rensselaer  Polytechnic  Institute,  1824-1894.. Small  8vo, 

Rostoski's  Serum  Diagnosis.     (Bolduan.) - i2mo, 

Rotherham*s  Emphasized  New  Testament Large  8vo, 

17 


50 
oo 
50 
oo 

00 
00 
00 


Steel's  Treatise  on  the  Diseases  of  the  Dog. 8vo,  3  50 

The  World's  Columbian  Exposition  of  1893 4to»  i  oo 

Von  Behring's  Suppression  of  Tuberculosis.     (Bolduan.) i2mo,  i  oo 

Winslow's  Elements  of  Applied  Microscopy i2mo,  i  50 

Worcester  and  Atkinson.     Small  Hospitals,  Establishment  and  Maintenance; 

Suggestions  for  Hospital  Architecture :  Plans  for  Small  Hospital.  i2mo,  i  25 


HEBREW  AND  CHALDEE  TEXT-BOOKS. 


Green's  Elementary  Hebrew  Grammar i2mo,  i  25 

Hebrew  Chrestomathy 8vo,  2  oo 

Gesenius's  Hebrew  and  Chaldee  Lexicon  to  the  Old  Testament  Scriptures. 

(Tregelles.) Small  4to,  half  morocco,  5  oo 

Xetteris's  Hebrew  Bible. 8vo,  2  25 

18 


